About the Author

My photo
Southport, Manitoba, Canada
Steve Pomroy is a professional flight instructor and aviation writer. He has been teaching since 1995 and holds an Airline Transport Pilot License, Class 1 Instructor and Aerobatic Instructor Ratings, military QFI, and an undergraduate degree in Mechanical Engineering. He's written and published three flight training books through his company, SkyWriters Publishing, and has several other books under development. Steve currently teaches RCAF pilot candidates on their Primary Flight Training course.

Monday, December 27, 2010


Well, Santa fell down on the job again this year and forgot to get me my new airplane....

Other than that, there's not much to write this week. But just wait'll you see what I've got lined up for the first third of 2011!

Happy Flying!

Saturday, December 25, 2010

Merry Xmas!

Merry Xmas, Folks! Hopefully Santa brought you some nice airplane stuff. I won't get to do any aerobtics today, but that's ok. I get to hang out around the tree with my ladies and pick up the flying on the 29th when I go back to work.

Merry Flying!

Wednesday, December 22, 2010

Aerobatic Prep

So the students here are all gone home for Xmas, leaving us to conduct proficiency flying and catch up on paperwork. Since I won't actually have any students of my own until after New Years, my paperwork load is pretty slim. That means I get to focus on getting ready for my Aerobatic Instructor flight test—if the weather changes, that is.

The problem, however, is that the weather isn't cooperating. It hasn't been for some time now. I had a 4 week stretch without flying during November/December thanks to the weather. Whenever it did clear up, students had priority. So since I don't have my own students, I got to sit on the ground. I got a couple of flights in a few days ago, and that's about it.

It's amazing how quickly g-tolerance deteriorates when you get out of practice. Ditto for maneuvering tolerance with regard to airsickness. It comes back fast, but the first hard aerobatic flight (or three) after an extended break can be pretty rough.

Unfortunately, the Grob isn't certified for snaprolls, instead they're a prohibited maneuver. It's too bad, since snaprolls are one of my favourite aerobatic maneuvers. The good news is that we can still do hammerheads (my second favorite!), and the other 8 maneuvers required on the ride (Spin, Barrel Roll, Slow Roll, Immelman, Split-S, 1/2 Cuban-8, 1/2 Reverse Cuban-8), not to mention a few others that can be flown just for fun.

Now if only the weather would clear up so I could fine-tune the maneuvers and the teaching...

Happy Flying!

Monday, December 20, 2010

Going in Circles (Lift Part 3)

In 2 earlier posts (here and here), I've talked about the equal-transit-time principle (wrong), Bernoulli' equation (right), and Newton's Second Law (also right). I've also mentioned "circulation" a couple of times, but haven't discussed what that means.

Circulation is a description of the flow velocity around a lifting wing. It is based on the superposition (i.e. - addition) of two flows: the straight freestream flow over the wing, and a rotating flow around the wing. The result of adding these two flows is that the flow over the top of the wing is moving faster and the flow under the bottom of the wing is moving slower. Throw Mr. Bernoulli into the mix now, and we can see that there will be lower pressure on top of the wing and higher pressure below the wing—thus we get lift. A really good bathtub experiment to demonstrate circulation is found HERE

I'm not a big fan of using circulation to explain lift to pilots. It's not that circulation is wrong, it isn't. The problem lies in the fact that in order to really understand circulation, way too much math is required. By "too much math", I mean large amounts of vector calculus. Incidentally, the phrase "too much math" isn't something you'll hear from me very often, so enjoy it while it lasts!

When using circulation to describe lift (for pilots), there is no explanation of where the circulation (i.e. - the rotating flow) comes from—it's just assumed to be there. The circulation has a physical origin, or course, but describing that origin requires a great deal of math, or a significant amount of physical reasoning—both of which are necessary for aircraft designers, but a waste of resources (in this case) for pilots.

Circulation is a component of potential flow theory. Potential flow theory, in turn, is founded upon continuity as one of the key underlying principles. So circulation can be viewed as a more complicated form of continuity. It turns out that if we aren't worried about number crunching and just want to know physical origins, continuity is a quicker, simpler way to meet our objective.

Circulation has the added disadvantage that it doesn't (without LOTS of math) explain the presence of the "adverse pressure gradient" on top of the wing. This adverse gradient is important as the principle source of stalling phenomenon. In turn, understanding stalls is one of the key reasons we need to understand lift.

Using continuity directly doesn't give us a way to calculate lift. That's a problem for the engineering folk. But it does provide pilots with a description of the physical origins of lift—which makes it a good description for pilots.

When reasoning through the lift-production process, you can choose to use either circulation or continuity to explain the flow velocity difference above and below the wing. But regardless of which approach you prefer, you still need Bernoulli to explain the pressure difference—which is really the key to lift.

The bottom line here is that circulation is a valid description of the flow around the wing, and can be used (in conjunction with Bernoulli) to describe the production of lift. However, it is not the optimum approach to use for the training of pilots. For that, we have the simplified approach using continuity—which provides us with a description of physical origins, but no tools to calculate lift.

When we need specific numbers (i.e. - the results of calculation and/or testing), we can go to the flight manual. This document is provided to us by the good folks who designed and/or manufactured the aircraft. In other words, we can let them worry about the hard math so we can focus on physical origins and useful rules of thumb.

Happy Flying!

Thursday, December 16, 2010

The Top 10 Christmas Gifts for a Pilot

Xmas is nearly here (9 more sleeps!). So it's probably past time to start thinking about what to get your favorite pilot for the big day. Nonetheless, if you're like me and prefer to do all of your Xmas shopping on the 24th in one big HURRAH, you might need some pointers. So, with that in mind, The Top 10 Christmas gifts for a Pilot:

Ok, I have to admit a little bias here. I don't really get airplanes that have to stay right-side-up all the time. What's the point of living in three dimensions and then handicapping yourself by cutting one of them off??? Real pilots do it inverted (for further on this, refer to last item on the list). In preparation for doing it inverted, this book will help your pilot develop an awareness and understanding of basic aerobatic maneuvers.

Pilots may sometimes seem superhuman (which, for some reason, non-pilots often refer to as inhuman, go figure), but they still gotta eat! The best place to eat is at or near an airport—especially after flying there. It's a law of nature. This handy guide will help with that.

In case your pilot gets lost, the Spot Satellite Messenger will help you find him/her. Of course, if you'd rather s/he stay lost, you can just ignore the text messages and emails it sends you.

Pilots like shiny things. Watches are shiny.

This particular watch is also useful: it tells time, it tells time (yes, it tells time twice), and it has a handy dandy flight computer build into the bezel—so your pilot can even do airplane stuff when s/he's not in an airplane.

For some reason, photography is a common hobby among pilots. It probably has something to do with having such a great view from one's office. I know at least 2 pilots who have gone pro and started making money off their picture-taking, and a multitude of others who are hard-core photo hobbyists, even on the ground. Your pilot probably already has a camera for taking simple snapshots. You need to get him/her something fancy! I'm a fan of the Canon Digital Rebel, since that's what I have (and for no other reason, really, no expert here).

As one of the reviewers says, "Don't buy these unless [your pilot] can handle copious amounts of awesome.".

And not just any flashlight will do. It has to be a Maglite. These things are bulletproof. Not that we usually carry bullets in airplanes. But we do usually carry pilots in airplanes, and these lights are even pilotproof. Simply amazing.

If you're shopping for me, this is the ticket! Pilots have all kinds of cool gadgets and stuff, and we need a cool bag to carry it all around in. Unlike many other flight bags, this one actually had some thought put into it's design. So it's built around the size, shape, and likely organization of pilot stuff.

Check out the demo video here.

Pilots love showing off, ahem, I mean, having passengers. Ask your pilot to take you up for a flight, then cover the costs of the trip.

And, the number 1 Xmas gift for your pilot:

Need I say more? Need details? Check it out here.

Note that this gift can be conveniently packaged together with the previous one.

Happy Flying!

Tuesday, December 14, 2010


Hey Folks. Heads up on FlightWriter's new address. We were previously located at http://flightwriter.blogspot.com. Now we're at http://www.flightwriter.com. Theoretically, the original addy should still work. And it does in that it will get you to the core content. But it seems that some of the widgets on the site don't work properly from there, and some others work intermittently. I'll try to get this fixed, but alas, my area of expertise is airplanes, not computers. So your best bet is to use the new addy: http://www.flightwriter.com!

All of the behind-the-scenes-computer-magic-infrastructure now seems to be worked out. If you use the http://flightwriter.blogspot.com address, it will automatically forward you to http://www.flightwriter.com.

Happy Flying!

Monday, December 13, 2010

Wherefore Art Thou Lift?! (Lift Part 2)

In my second-to-last post, I looked at the equal-transit-time concept of lift production (and, for those who didn't read the post, pointed out that it's incorrect). I also mentioned a few things that I hear in theory-of-flight "discussions" that annoy me. The equal-transit-time concept and associated remarks were on that list. Some other important pet peeves included:
  1. Bernoulli is "just a theory" and has never been proven,
  2. If Bernoulli were right, it wouldn't be possible to fly inverted, and
  3. 80% of lift comes from Bernoulli, 20% comes from Newton (or some other set of false numbers).
First things first. "Prove: to test, prove worthy" (from www.etymonline.com. To say that something is "just a theory" and "has never been proven" is a contradiction. If an idea has never been proven (as in tested), it isn't a theory, it's a hypothesis. Theories have been tested, repeatedly, against logical consistency and empirical evidence. To become a theory, a hypothesis must survive this repeated testing and never be "disproved". The "just a theory" nonesense gets used a lot by people who have a personal preference or political agenda that is contradicted by the facts. It shows up all the time in the ongoing religion-v-evolution "debate", but I digress...

Based on this (proper) definition, Bernoulli's Equation indeed qualifies as a 'theory'. It is not a hypothesis. Has Bernoullis' equation been tested against logical consistency? Yes. Has it been tested against empirical evidence? Yes. Has it ever failed a test (i.e. - been disproved)? No. So, is Bernoulli's equation right? Yes, within the limits of the approximations made to get it (no friction and no compressibility). Can it be used to calculate (or explain the physical mechanism of) pressure changes around a wing? Yes, at low Mach numbers (where compressibility is unimportant) and low angles of attack (where friction effects are low and there is no airflow separation).

At higher Mach numbers and in the presence of friction, Bernoulli can still be used if we ("we" being the engineers who do these types of calculations) apply the appropriate corrections. From the standpoint of describing the physical mechanism of lift (i.e. - no number crunching), Bernoulli is useful right up until shock waves start to appear in the high-speed range, and until large amounts of separation result in stalling in the low-speed range.

Beyond empirical testing in the physical world, Bernoulli's equation can be derived from Newton's Second law of Motion. Applying Newton's Law to a fluid element traveling along a streamline in the absence of friction (i.e. - outside the boundary layer) will yield Euler's Equation. Applying this equation further to an incompressible fluid (i.e. - a fluid of constant density) will yield Bernoulli's equation. So the argument that lift comes from Newton, and not Bernoulli is silly, since they are both ultimately the same thing: Newton describes the conservation of momentum, and Bernoulli describes the conservation of energy (as applied to a flowing fluid).

Bernoulli's Equation tells us that as fluid's velocity increases, static pressure decreases. This is ultimately the source of lift on an aircraft wing. The question, then, is, "Where does the velocity change come from?" (Answer: Not equal-transit-time!). Bernoulli's equation says nothing about this. It just states that given a velocity change, there will be a corresponding pressure change.

The velocity change comes from the shape and angle of attack of the wing. The flow of a fluid is governed by the principle of continuity, which, boiled down to it's most fundamental form, is the conservation of mass applied to a flowing fluid. Without getting into details (maybe in a future post), continuity will result in increased velocity over the top of a positively cambered wing at a positive angle of attack.

Ok, so what about downwash and Newton's Third Law? Forces occur in equal and opposite pairs. So if the air exerts a force on the wing, the wing exerts an equal and opposite force on the air. As the wing gets pushed up, the air gets pushed down. How does this all come about? The pressure differnces above and below the wing result in the formation of wingtip vortices. These vortices create an imbalance between the upwash (ahead of the wing) and the downwash (behind the wing) so that there is an excess of downwash. The net effect is for the air in the vicinity of the wing to be deflected downward. But this deflection ultimatly requires the pressure difference above and below the wing—which is calculated/explained by Bernoulli's equation.

This addresses the (non-existent) 80/20 split between Newton and Bernoulli. The physical mechanism of lift can be described in terms of Newton (redirected airflow and action-reaction force pairs) or Bernoulli (velocity changes resulting in pressure changes). Both descriptions are valid, but they don't share the labor. If you know the velocity change and mass flow in the downwash, you could calculate the lift being produced. On the other hand, if you know the velocity changes, and therefore the pressure changes, over the wing, you could calculate the lift being produced. Both approaches would give you the same result, and that result would match measurements of the lift on the wing in question.

What about flying inverted? Well, to quote myself from above, "The velocity change comes from the shape and angle of attack of the wing", and "...will result in increased velocity over the top of a positively cambered wing at a positive angle of attack" [emphasis added in both quotes]. What about at negative angles of attack? The positive camber will induce higher velocities on top of the wing even at low and zero AOA. But if the AOA gets sufficiently negative, the wing will produce negative lift due to increased flow velocity over the bottom of the wing. Positively cambered wings aren't very efficient at producing negative lift, but they can do it—and this is indeed consistent with Bernoulli's equation (or, more correctly, continuity/circulation as a source of velocity change).

Great. Now, what about "Circulation"? It's been mentioned a little bit here, but the details will have to wait till next post! Till Then:

Happy Flying!

Friday, December 10, 2010

Dead Links

I discovered last night that there were a bunch of dead links in some of my earlier posts. The problem was that Blogger inserted extra text into several of the links trying to link back to the blog itself. I think I have them fixed now. So if you had trouble getting to external links previously, go back and try them again. They should work now.

Happy Flying!

Thursday, December 9, 2010

The Straw Man of "Equal Transit Time" (Lift Part 1)

Over the years, I've had the misfortune of hearing far too many arguments about where lift on a wing comes from. The whole debate has become something of a pet peeve of mine, because it's all nonsense. I can't stand listening to people try to present themselves as experts, and supporting the position by making false (and often outright ridiculous!) statements. Does this make me a negative person?

Some of the silliness out there includes things like:
  1. "Equal Transit Time" is wrong, therefore Bernoulli is wrong,
  2. "Equal Transit Time" is right,
  3. Bernoulli is "just a theory" and has never been proven,
  4. If Bernoulli were right, it wouldn't be possible to fly inverted, and
  5. 80% of lift comes from Bernoulli, 20% comes from Newton.
For number 5, the numbers vary, but the wrongness is all the same. Is "wrongness" a word? According to spellchecker it is, but I'm not so sure...

The "Equal Transit Time" of points 1 and 2 is a fallacy that has (fortunately!) fallen into disrepute over the years. But it still gets set up as a straw-man to "disprove" Bernoulli. According to the equal-transit-time principle, the air particles that separate at the leading edge of the wing must meet up again at the trailing edge. So, because of the wing's curvature (the top surface is longer than the bottom surface), the over-top flow must travel faster than the under-bottom flow.

Unfortunately, there is no physical principle that requires air parcels to meet up again once they are separated. In fact, wind tunnel testing (among other methods available) can and has demonstrated conclusively that the equal-transit-time requirement is not met by a lift-producing airfoil—the over-top air travels significantly faster than the under-bottom flow and reaches the trailing edge first (see a useful NASA applet here).

Ok. So equal-transit-time is wrong. So far so good. But here's the problem: Several authors and educators have taken the position that since equal-transit-time is wrong, Bernoulli must also be wrong. The "reasoning" (and I use the term in the loosest possible way) is that equal-transit-time leads into Bernoulli by supplying a source of velocity difference, which is then converted into a pressure difference using Bernoulli (higher velocity over-top means lower pressure over-top). So if the source of the velocity difference is wrong, the pressure conversion must also be wrong. Right? Wrong!

The change in velocity and the change in pressure are two different phenomena that require two separate explanations. There is in fact a velocity difference above and below a wing. And that velocity difference does in fact result in a pressure difference a-la Daniel Bernoulli. It's just that the velocity difference is not explained by the equal-transit-time concept—instead, it must be explained by the principle of continuity, or circulation (which, in turn, is rooted in continuity anyway).

More on Mr. Bernoulli and Sir Isaac in my next post. And for those of you who insist on discussing Circulation, don't fret! I haven't forgotten you!

Happy Flying!

Sunday, December 5, 2010

The Top 10 Considerations for Winter Operations

Well, winter is certainly here. At least it's here on the prairies, and here to stay. We had a -18C day today. I'm new to the prairies, but I'm told it gets quite a bit worse... That would be ok if the wind would just stop filling my driveway with snowdrifts!

So, since winter is here, it's time to have a good look at winter ops. A quick and easy way to do that is with a top 10 list. So, without further ado, the top 10 considerations for Winter Operations (in no particular order):
Engine (and Battery!) Pre-Heat

Engines can be finicky when they're cold. The two main problems are the oil viscosity (although this problem is reduced with modern, multi-viscosity oils) and the reduced vaporization of the fuel—liquid fuel doesn't burn, it must vaporize and mix with air first. These problems are aggravated by reduced battery performance in cold conditions.

To improve the start-up reliability of an engine in cold weather, pre-heat the engine before starting. The easiest way to pre-heat is in a warm hangar, but an engine heater can also be used. An engine heater is simply a supply of warm air (warmed electrically or by combustion) pumped into the engine cowling. Heater effectiveness can be improved by using a cowl cover—which is essentially a form-fitted blanket that wraps around the engine cowl to help trap heat. Having a cowl cover provides the extra advantage that during short turnarounds, the cowl cover can help the engine hold the heat from the previous flight, thus eliminating the need for an engine heater.

Engine Warm-Up on Start

After the engine is running, it still needs time to come up to full operating temperatures. As long as there are strong temperature gradients in the engine, there will be unnecessary mechanical stresses. Running the engine at high power settings prematurely can lead to damage and a need for extra maintenance and/or early overhaul. Hopefully, you have a cylinder head temperature gauge, as this is the most important temperature indication for winter ops. But if you don't you'll need to use oil temperature as a proxy. This is less accurate and less reliable, but sometimes a necessary evil.

There is some good information on engine pre-heat, start-up, and warm-up HERE.

Shock Cooling

Shock cooling of piston engines during prolonged descents is always a concern. But it becomes much more of a concern during winter ops thanks to the increased temperature difference between the engine and the cooling air. Having a winterization kit helps (by reducing the cooling airflow) if that's available, as does closing the cowl flaps if you have them. But in any case, you should carry partial-power during all descents. If that won't get you down fast enough, use flaps, gear, spoilers, or a finer propeller setting—or even better, fine-tune your descent planning and start down sooner.

It's also a good idea to warm the engine by spending a few seconds at cruise power (or full power for lower-powered engines such as those on most trainers) every couple of minutes. This can be referenced to altitude instead of time (for example, every 500 or 1,000 feet) for the sake of keeping track.

Warming the engine has the added benefit of confirming that the engine is still actually running. At low power settings in a descent, an engine failure may be difficult to recognize. Further, as the engine cools, the quality of combustion in the cylinders can be reduced—sometimes resulting in an outright engine failure. Identifying a failure sooner means you have more time (and altitude!) to deal with it.

Note that there's a pretty good argument against the very existence of shock cooling HERE, but until more data is in regarding the problem, I'd stick with conventional wisdom. Worst-case-scenario then is that you're erring on the side of caution—not a bad course of action in an airplane!

Critical Surface Contamination

Surface contamination can occur year-round in flight under the right conditions. But only during winter operations will you see frost and icing on the ground. Inspecting for and eliminating this contamination is a vital part of your winter pre-flight inspection.

Surface contamination has two key and detrimental effects—it increases drag and decreases lift. The ultimate effect of both of these is to degrade performance—sometimes to the point where retaining control or remaining airborne become impossible. Surface contamination will result in reduced cruise speed, reduced climb rates, reduced glide range, increased stall speed, increased takeoff distance, and the potential for control malfunctions—including things like aileron reversal and tail stall

Dealing with in-flight icing is a topic unto itself, and is briefly touched upon below. But dealing with ground icing is easy—get rid of it. Any adhering ice or snow (including frost) should be removed from your aircraft before departure. You can do this during pre-flight with brushes and scrapers or in a warm hangar, or you can get your aircraft de-iced with de-ice fluids before takeoff. The choice between these two approaches will depend on the available facilities and your available budget. Either way, plan ahead and make sure your schedule accounts for the time required and that you have the required equipment.

Further information regarding ground icing can be found in NASA's excellent online course right here.

Runway Contamination

Contaminants on the runway (water, slush, snow, ice) can hit you with a good one-two punch. They degrade acceleration (on take-off) and deceleration (on landing) plus, they degrade directional control. This can result in performance degradations leading to runway over-runs, or loss of control resulting in going off the edge of the runway. In extreme cases of landing on thick snow, the result can even be flipping over and stopping very short after the landing gear digs in.

Avoiding runway contamination completely isn't always an option. So the key is to be aware of contamination present and to be familiar with your aircraft's limitations (and your own!). When considering these limitations, don't forget to account for the crosswind component and the gustiness of the winds.

At airports with ground facilities, such as control towers or flight service stations, advanced notice of surface contamination is often available in the form of Runway Surface Condition (RSC) reports. At uncontrolled aerodromes with no ground stations available, you may be able to get reports from other pilots who have taken off or landed there recently. In the absence of these reports (or if you doubt their reliability), a precautionary inspection of the surface is called for. If you're taking off, this can be done by taxiing (or in extreme cases, walking) the length of the runway. If you're landing, conducting a low-level inspection would be prudent—as would including fuel for a possible diversion in your flight planning

Airborne Icing

Airborne icing can occur year-round, so it really isn't a winter-specific problem. However, it is more common during the winter. It's also far more likely in the winter to occur outside of cloud—for example, in precipitation or mist—making it a much more significant concern for VFR pilots during winter than during summer.

Unless you are in an aircraft equipped for icing conditions and you have received training in operating that equipment and dealing with in-flight ice, the best way to deal with the ice is to avoid it. This means checking forecasts and reports thoroughly prior to departure. It means getting weather updates while en-route. And it means developing an in-depth understanding of the weather and the conditions that may lead to icing.

If you find yourself in icing conditions (without the equipment or training to deal with it), deal with the problem like any other emergency—and yes, this is an emergency—keep flying the plane, and assess before acting rashly. It's often a good idea to undo the last thing you did. If you were in cruise when you entered ice, turn around. If you were climbing, descend. If you were descending, climb (if you still can).

In any case, your objective needs to be met in two steps: first, stop any further ice accumulation; second, get rid of the ice you have. The first step means getting away from liquid water. The second means finding some warmer and drier air to get the ice to sublimate off. Both of these objectives can often (but not always) be met by changing altitudes. As you're dealing with the problem, talk to ATS and/or other pilots to get more information on where the icing conditions are. Also, pass the word on so other pilots can avoid the conditions you've found yourself in.

Further information regarding in-flight icing can be found in NASA's excellent online course right here.

Cold Weather Survival

If you're lucky, you get to do your pre-flight inspection in a warm hangar, and you have an airplane with a good heater. That makes winter flying much more comfortable and enjoyable. However, it can lull you into a false sense of security. If your heater fails (or if you have to shut it off due to CO poisoning, discussed below), or worse, if your engine fails and you have to spend a night in the woods, you'll be very sad if you only dressed for a warm hangar and a good heater. If you're lucky this time, you'll only lose your fingers and toes to frostbite. If you're not so lucky, Search and Rescue will become Search and Recovery. Even barring an emergency, un-forecast weather can force you to make an unplanned landing off-field or on a small middle-of-nowhere aerodrome with no facilities.

Keeping all of this in mind, you should always be dressed for the walk home. Sure, you can (and should) store some extra stuff (including blankets and fire starter) in the back. But imagine crashing and being pinned in your seat unable to reach that stuff in the back—or narrowly escaping from burning wreckage only to watch your blankets go up in smoke. Won't you be glad you turned the heat down and wore some extra clothing while flying?

Cold weather survival is something that deserves attention during winter ops. I recently heard a statistic from some military folks: Average Search and Rescue time is 48 hours. So if you're on the ground and nowhere near civilization, you need a way to keep warm.

Spatial Disorientation due to Whiteout

Whiteout occurs when an overcast sky visually merges with a featureless, snow-covered ground—eliminating the horizon from a pilot's visual reference. This condition can lead to spatial disorientation and a subsequent loss of control, even in clear weather with good visibility. The problem can be compounded by empty field myopia, which sets in in the absence of features to focus on. Whiteout can also be aggravated by reductions in visibility, especially by falling snow, even when light.

Increased instrument reference is a must in whiteout conditions. If you find yourself disoriented, try to change directions (with instrument reference) to find ground features that will help you regain orientation. Hills, mountains, heavily forested areas, bodies of water that haven't frozen yet, large built-up areas, etc. can help break up the snow cover of the ground, and thus reduce or eliminate the whiteout.

Carbon Monoxide Poisoning

In the winter, we tend to seal up the cabin as best we can, and fly with the heat on. There's a good reason for this: It's COLD! The downside to this quest for warmth is that it increases the risk of CO poisoning. Heat is supplied either by a heat shroud over the exhaust manifold/pipe, or by a combustion heater. Either way, there's a risk of combustion products leaking into the cabin.

The best way to deal with this risk is to be equipped with a CO detector. The detector you use should be sensitive enough that it will sound the alarm before any negative physiological effects kick in. And what do you do when (if) the alarm goes off? 1) Turn off the heat, 2) Open the vents and windows, 3) Land. Yes, it's going to get cold. So dress for the walk home.

The Pre-Flight Inspection

Although we've already looked at the engine and battery pre-heat, as well as critical surface contamination—both of which are key elements of the pre-flight inspection—it's worth revisiting the pre-flight from a broader, human factors, perspective. It's cold out! Human nature being what it is, cold is a strong motivator to hurry it up and take shortcuts. It also creates a significant distraction—we focus on staying warm instead of inspecting the aircraft. In a word, this is dangerous.

There are two key steps to addressing this problem. The first is to be aware that there is in fact a problem and to make a conscious effort to focus on the task at hand (i.e. – the pre-flight inspection). The second step is to dress warm. If you're dressed for the weather, the weather will be less of an impediment for you. This goes back to cold weather survival, too. If you're carrying winter gear for an emergency, why not use it for normal operations as well?

An even better solution, when the option is available, is to complete your pre-flight inspection inside a heated hangar. This keeps you warm—helping ensure a quality inspection—and it keeps the engine warm until it has to go outside.

Wednesday, December 1, 2010

The Myth of Centrifugal "Force"

As a follow-up to a previous post on Equilibrium, I thought I'd talk a little bit about a common non-equilibrium maneuver—the steady turn. Much of what is said here can also be applied to pitching maneuvers—in fact, any maneuver that involves a curved flight path and the associated accelerations.

Our interest in turns, for today, stems from the often-debated "Centrifugal Force". Centrifugal Force is "often-debated" because there are those who claim that it doesn't exist, while other insist that it must because you can "feel" it in a turn. From the title of this post, you can probably guess which camp I fall into. I would argue that centrifugal force does not exist. However, in fairness tho those who disagree, it really does depend on your perspective (I'll clarify that shortly). And we'll see that centrifugal force is still a useful concept when considering objects that are moving in a circle.

Centrifugal force fits into a category of forces that physicists call "pseudo-forces", and engineers call "inertial forces". these forces exist—in that they can be both calculated and measured—only if you are using an accelerating object as your reference (a "non-inertial reference frame" in technical terms). Normally, we measure position, velocity, and acceleration from a position of equilibrium. In this case, the position and velocity of an object might vary depending on our reference, but the acceleration will always be the same.

This changes if we measure or observe from an accelerating reference. Measuring the acceleration of an object from an accelerating reference means that we will get a different value than someone else measuring the same acceleration from a different reference (either in equilibrium or accelerating differently). Inertial forces, including centrifugal force, ultimately stem from this discrepancy—recall (from Newton's Second Law of Motion) that acceleration is closely related to forces.

Let's consider what happens in a car going around a turn (we'll use a car here instead of an airplane in order to eliminate the small complication that comes from considering bank angle). When you're sitting in a moving car and the car is taken around a turn, you feel yourself being "pulled" to the outside of the turn. That sensation is very real. The problem is that your frame of reference—the car—is not in equilibrium. The physical sensation of centrifugal force is in fact the sensation of the car pushing you into the turn. An observer outside, sitting on the curb and in equilibrium, sees the friction on the tires pushing the car into the turn, and sees the car seat (and associated hardware) pushing you into the turn. No forces are present directed to the outside of the turn.

The same principle applies in an airplane, except that we turn in a banked attitude, so the "force" that we feel is directed straight down through the floor of the aircraft, not to the side (assuming the turn is coordinated—a topic for another day). Ditto for wings-level pitching maneuvers—such as entering or exiting climbs or descents, or aerobatic maneuvers such as loops.

In practice, the importance of Centrifugal "Force" is in it's relationship to load factor. Load factor is a measure of the aircraft's "normal" acceleration—where "normal" means perpendicular to the flight path. There's a limit to how much load factor we can take. At low speeds, we eventually reach the stall limit. At high speeds, we eventually reach the structural limit. At any speed we might reach our own physiological limit (grey-out – black-out – G-LOC), which can vary significantly from person to person. Load factor is controlled by controlling lift. At any given airspeed, lift—and therefore load factor—is controlled by Angle of Attack.

Is Centrifugal Force real or isn't it? Well, when you're sitting in an aircraft pulling 6 g's it certainly feels real! The structural loads are real, the physiological effects are real. So at the very least, the concept is useful. Perceiving the aircraft as if it were in equilibrium with a new "gravity" force may be easier on the brain than keeping track of all the physics of flight—especially while simultaneously trying to stay oriented and maintain control!

So the bottom line here is that Centrifugal Force is not truly a force, but it's still a useful concept. It simplifies our picture of the world and helps reduce the brain power dedicated to things other than flying the airplane. But if you want to hangar fly and argue the nitty-gritty of flight theory, it really doesn't exist!

Happy Flying!

Monday, November 29, 2010

Vitamin 'g' Shortage

It's been a pretty slow week here. The weather (snow, snow, and more snow) has had us grounded for almost two weeks. Every now and then it clears up for half a day, but the students get priority and I don't get to fly. I won't have any of my own students until after the New Year. In the meantime, I'm trying to get my Aerobatic Instructor Rating out of the way. That was going well for a while, but now progress has stalled. All this lack of flying is making me feel very rusty!

It's funny how, when it's not that busy (like now!), my motivation to write all but disappears. I should be getting lots of posting done, but here I am writing a filler post a week after my last. But fear not! My next real post is started, and will be here in the (hopefully) not-too-distant future. TEASER: It's a follow up from my last post on equilibrium, and is a brief discussion of "centrifugal force".

Happy Flying!

Monday, November 22, 2010


Equilibrium is one of those areas that many new student pilots have trouble understanding. It's actually a pretty simple concept, but we tend to over-complicate these things sometimes. If we want to be picky about our terminology, we really should use the term "mechanical equilibrium". But since we don't normally talk about other forms of equilibrium in aviation (e.g. – hydrostatic, thermal, chemical, etc.), we can stick to the shortened and more generic "equilibrium".

So, equilibrium (the mechanical kind) refers to the absence of acceleration. If we think in terms of Newton's Laws of motion, this suggests that there are no net forces acting on the aircraft—so all of the forces balance (cancel out) and the aircraft will travel in a straight line at a constant speed.

That seems pretty simple (and it is!), but the confusion comes from our intuitive understanding. Equilibrium is often considered (intuitively) to refer to a stationary object—which isn't a requirement at all. We generally don't have trouble extending this intuitive concept to steady straight-and-level flight. But we often run into trouble trying to apply it to climbs and descents.

The "logic" (for lack of a better term) applied seems to be that if the altitude is changing, there must be acceleration, and we therefore must not be in equilibrium. This is wrong. In a steady climb or steady descent, there are no net forces acting on the aircraft, and there are therefore no accelerations.

So straight steady climbs and descents are included in the list of maneuvers that qualifiy as equilibrium—along with straight & level at constant airspeed and sitting stationary on the ramp (and hovering if you fly helicopters). However, the transition from straight & level into a climb/descent is not equilibrium, nor is the transition back into straight & level.

Why is this important? Well, equilibrium (or the lack thereof) is related to the forces acting on the aircraft. We need to be conscious of these forces in order to anticipate aircraft behavior. This is especially important at low speeds, where an increase in lift brings us closer to the stall. If we have more lift than weight, then we are not in equilibrium, and the stall speed is increased. This will happen when we make adjustments to the flight path using pitch.

Happy Flying!

Thursday, November 18, 2010

Air Cadets

Since we’ve recently passed Armistice Day, this seems like a good time to write a quick note about the Cadet program. Although I would consider all of the Cadet programs (Army, Air, Sea) to be outstanding, my own experience was with Air Cadets . So, in keeping with the flying theme of this blog, I’ll focus on Air Cadets .

The most obvious statement that can be made about Air Cadets is that you can learn to fly through the program at no (financial) cost to yourself. The Air Cadets have a Gliding Scholarship program, through which you can go on a summer course and get your Glider License, and subsequently be presented with your Glider Wings. Also, they have a Flying Scholarship program, through which you can go on a summer course and get your Private Pilot License, and subsequently be presented with your “Power” wings. Getting to go on either of these programs is competitive and requires you to participate in a squadron level groundschool course, write an entrance exam, and participate in a board interview. The competition process itself is a valuable learning experience, and even if you don’t get to go on course, you can try again the next year.

Aside from the opportunity to fly, the Cadet program offers a whole host of other activities and benefits—not the least of which is a host of summer courses, varying in length from 2 to 6 weeks, to help cadets develop a variety of skills, including: leadership and instruction, musical ability, wilderness survival, and introductory courses in things such as aircraft maintenance and air traffic control. At the squadron level (meaning at home, not on a summer course), the Cadet program offers sports, compulsory and optional training activities, wilderness outings, and a variety of opportunities for personal growth. Perhaps the most significant of the personal growth experiences is the progressive responsibility earned as leadership skills are developed and rank is increased.

A good friend of mine, who never learned to fly through Cadets, but later paid his own way through flight training, once commented on the value he received from Cadets. He noted that even though he hadn’t learned to fly through them, he wouldn’t consider trading the experience for anything. The life skills obtained from the Cadet program were invaluable.

Surely, the most expensive benefit I received from Cadets was my Private Pilot License. But when I set financial considerations aside, I see many other treasures I obtained from my cadet experience. My early development as a leader, teacher, and citizen were almost exclusively the result of my Cadet experience. None of these things were (or are) provided by our public or post-secondary education system.

The Cadet program is considered to be a “paramilitary” organization in that they wear military uniforms, participate in military formalities such as marching and saluting, and use a military style rank structure. However, cadets do not receive any combat training and are under no obligation to join the Regular Forces or Reserves later in life. This is a common misunderstanding among parents. I had at least two friends growing up who were not permitted to join Cadets because their parents were certain they’d be required to join the Army later on. This fear is completely unfounded. The Cadet program is, first and foremost, a youth organization.

If you are between 12 and 18, you should look into the Cadet program and consider joining. If you’re older, you should consider how you might contribute. Leadership in the Cadet program comes primarily from the Cadet Instructor Cadre (CIC). Civilian positions are also sometimes available.

Happy Flying!

Thursday, November 11, 2010

Armastice Day

In 2005, I took a trip to France just a week or so before Armistice Day. The trip was for myself and two coworkers to receive training in a software package called CATIA. But we went a week early so that we could vacation a little and see the country. When we first arrived, we went our separate ways, and then met up again in Paris a week later for our course.

My wife and I went to Normandy. We stayed in Bayeaux and toured around from there. One of the major attractions of Normandy, of course, is the D-Day beaches. We got to visit Omaha, Utah, and Juno, but missed out on Gold. Juno, of course, was of particular interest, because it’s where the Canadians came ashore. At both Juno and Omaha, I stood in the water and looked inland to see what the soldiers saw. At Omaha, it was a vast flat beach with no cover. At Juno, it was a steep sea wall close to the beach. In either case, I wouldn’t want to have to make the crossing with a bunch of angry machine gunners on the other side.

There are plenty of preserved memories of the war. These include naval barges that were sunk in shallow water to create mini-islands and give landing craft some cover, concrete bunkers used as part of the German defenses, and giant craters created by naval artillery meant to suppress German defenses.

Looking at the area now, you’d never say that it was once the scene of such violence. It is beautiful and peaceful there. It’s the kind of place I’d like to retire to someday.

One thing that surprised me was how many German people were there to see the sights. Of course, Germany is right next-door to France, so it really shouldn’t have been that surprising. But it was. Several of them seemed very regretful over the war. One older gentleman (not old enough to be a veteran, but older than me, perhaps a child during the war) mentioned that he visited these beaches regularly to remind himself that "we must never let this happen again".

Sure enough, the preserved evidence of the violence is very convincing. As peaceful as the area is now, there’s enough information available, and enough preserved scarring, to convince anyone that we can do without a repeat. So today, take a moment to remember those who put themselves at risk, some of whom paid the ultimate price, to preserve and protect our way of life. Then take a moment to remember those currently serving in Afghanistan.

Happy Flying!

Tuesday, November 9, 2010

Piloting as a Profession: Part 5, More on Training Standards

... Continuing from the previous post (Part 4, Training Standards) and considering the question, "What single change could be made that would result in the most improvement in the flight training industry?":

The whole point of training is to enable students to learn from the experience of others. This suggests that we need experienced instructors, who can then pass on that experience for their students’ to benefit. So, the most important thing we need is better trained and more experienced instructors. An instructor who just barely has a Commercial Pilot License is not usually capable of providing high-quality instruction. 200 hours (ok, 230 hours) really isn’t enough time for an instructor to build up their own experience bank to draw upon when teaching.

This wasn’t always the case. When the training paradigm currently used in aviation was developed, 200 hour pilots had flown multiple high-speed, complex aircraft and had survived over 100 hours of combat. The very fact that they were alive provided a testament to their abilities and experience. No such filter exists today (thankfully!).

Does this mean that a 200 hour pilot can’t be a good instructor? Of course not. Notice that I said "usually". But making policy or regulations based on the occasional exception is a poor approach to quality control.

Increasing the experience requirements for instructors doesn’t just get us better instructors through a direct increase in experience. It also impacts motivation. If the experience requirement is increased enough, it cuts off instruction as an entry level job for time-builders. By the time an instructor candidate is qualified to teach, they will have enough flight time to have other career-path options. This means we’ll only get instructors who want to teach. Right now, there are far too many instructors who just want to get hours at somebody else’s expense—they don’t really want to teach. More often than not, this motivation shows up in the quality of work. So we often have a compound problem in that an inexperienced instructor (who is already limited by a lack of experience) also doesn’t want to teach. Both aspects of this problem can be eliminated, or at least significantly reduced, by a large increase in instructor experience requirements.

So how much experience should be required of instructor candidates? I don’t know, but I think it’s a question worth investigating. I’m inclined to suggest that an ATPL should be required for an instructor rating. But I don’t have any facts or figures to support this, it’s just a gut instinct.

Are there any "cons" to this approach? Certainly. The only significant one I can think of is in the training of Private Pilots. Increasing instructor experience requirements will also increase the cost of training, since the instructors will be paid better. I’m loath to suggest changes that will drive up the cost of training, as it is expensive enough as it is. But short of having different instructor qualifications for teaching PPL and CPL candidates (I don’t think this would work very well), I don’t see a way around the cost increase.

But what about all those pilot wannabe’s that now can’t live the dream because we’ve cut off the primary time-building option? Nonsense. This "problem" will quickly sort itself out through changes in the supply and demand dynamic. What will actually happen is that pilots fresh out of flight school will have the opportunity to fly Part VII operations much more quickly because the supply of high-time ex-instructors will disappear. Will this negatively impact safety? No, because the increase in the quality of training will cover the shortfall of experience—that’s the whole point of the change. Will there be an adjustment period? Yes, and it will have to be managed carefully.

Will this change, in and of itself, fix everything? Nope. There are changes needed in the training program and completion standard for both the CPL and the ATPL. However, this one change would fix many of the problems we see. Further, outside the training industry, there are changes needed to improve the industry overall (duty time limits and whistleblower protections come to mind).


Happy Flying!

Sunday, November 7, 2010

Piloting as a Profession: Part 4, Training Standards

... Continuing from the previous post (Part 3, Self Regulation) and considering the question, “Is the training/education provided to pilots adequate?”:

Transport Canada and the Transportation Safety Board have recognized that a statistical up-tick in accident rates occurs at around 500 hours of total flight experience. It is believed (but not actually known for sure) by many that this up-tick is a result of confidence exceeding ability. Of course, even if this is accurate, it’s surely an over-simplification, but it’ll do for our present discussion. 500 hours puts a full-time new-hire pilot about 3 to 6 months out of school. Having an accident rate problem at this point is a clear symptom of weaknesses in training.

Some other symptoms of weak training include:
  1. Fail rate (~25%!) on a flight test that some in the industry consider inadequate to begin with.
  2. Fail rate (~32%!) on a "written exam" that many (most?) in the industry consider inadequate to begin with.
  3. Insurance requirements tied to raw experience with no reference to education.
  4. Employability requirements tied to raw experience with little or no reference to education.
This last one is especially important. When people within the industry don’t value or recognize the education received by pilots, that presents us with a big red flag.

Do some pilots work hard and learn lots and excel at what they do? Yes. Absolutely. Do some others do the minimum required of them and scrape by on a fairly low standard? Yes. Definitely. But how many wash out due to lack of effort or aptitude? I don’t have any numbers, but from my own experiences and observations, I feel confident saying "not very many".

One of the problems we run into is that companies have no way to distinguish between the "high quality" and "low quality" pilot groups—they all get the same license in the end. As a result, there is no incentive to hire, promote, or pay extra for the higher quality candidates. The absence of quality incentives discourages high quality candidates, and even pushes some of them out of the industry altogether. This creates a vicious circle caused ultimately by what economists term "information asymmetry"—resulting in the long-term degradation of the average quality of pilot candidates. How many potential high-quality candidates chose to pursue business, medicine, or engineering instead of aviation after hearing about the widely publicized pay rates and working conditions of the Colgan 3407 pilots. (That’s a rhetorical question, I don’t actually have any stats, but there’s no doubt that there were many).

This gradual degradation of the quality of pilot candidates is a long-term industry risk that is hard to recognize, in part because it has no corresponding short-term risk. Further, the risk is amplified by the rarity of high-quality training.

I mentioned previously that the training philosophy in aviation hasn’t changed appreciably since World War II. This isn’t all bad. The fact is, the framework that we conduct training within is pretty effective. But there is room for major improvements, and some changes are long overdue—especially in the training of professional pilots (in truth, the training of private and recreational pilots is pretty good, and probably doesn’t need any direct changes).

So, bearing all of this in mind, what changes should be made? This question opens a huge can of worms. The list could be very extensive and subject to all kinds of debate. Changes suggested could range from fundamental changes to minor fine-tunings, with everything in between. So, for the sake of brevity, I’ll take a more focused approach to the question.

Instructors are taught very early on to look for the "root cause" of student errors. A single root cause often results in a series of errors. So rather than trying to fix each error independently, we should try to address the one error (i.e. – the root cause) that will fix the most subsequent problems. With this philosophy in mind, what single change could be made that would result in the most improvement in the flight training industry? (Note that even this approach will give us a debatable answer to the question, but at least the debate can be a little more focused).


Happy Flying!

Friday, November 5, 2010

Piloting as a Profession: Part 3, Self Regulation

... Continuing from the previous post (Part 2, Are We Professional?) and considering the question, "Can pilots self-regulate without compromising public safety?":

There has been lot’s of debate over the aviation industry’s ability to self-regulate. There are all kinds of theoretical reasons why we shouldn’t be allowed to self-regulate—most of them based on flawed or incomplete theory, frankly. But, as they say in engineering, data trumps theory. There are plenty of other disciplines where self-regulation has been successful and effective—medicine and engineering come immediately to mind, but there have been others as well.

One of the problems with the self-regulation concept is that many people interpret "self-regulation" as "no rules and no oversight", which would indeed be likely to cause problems. In fact, there have been examples of this approach, and they have invariably proved unsuccessful. So, in order to effectively discuss self-regulation, it’s important to clarify what self-regulation means, and to make a distinction between different approaches.

One example of self-regulation is what we are seeing with the implementation of SMS (Safety Management System for readers not familiar). SMS basically amounts to individual companies regulating themselves without oversight from regulatory authorities or other industry groups (some regulators may disagree with me on this point, but let’s call a spade a spade—any oversight that exists is superficial at best). Some companies are really good at regulating themselves, and they make SMS look good. Some other companies are ... um ... not so good, and SMS gives them the opportunity to get worse. The program has been roundly criticized by the Auditor General, primarily due to the lack of proper oversight. Similar criticisms have been forthcoming from industry insiders.

This SMS-based example is distinct from the self-regulation of a profession. The self-regulation model of a College is that of a whole industry self-regulating with legislative oversight from parliament. A whole industry necessarily takes the long-term view when making decisions. This may not be the case for individual companies. Further, the interests of a whole industry are far more likely to be aligned with the interests of society than those of a single company. There are certainly counter-examples of this (for example, I could now rant about the ongoing and unnecessary shortage of doctors in Canada), which is why oversight is needed, but the general trend is valid.

Bearing this distinction in mind, could pilots, as an industry-wide group, successfully self-regulate? Could they balance the needs of the profession and industry against the needs of society?

If you’re of the mind that pilots cannot self-regulate, then I would have to ask, "Who should regulate us?". Who should regulate the operation of complex machinery, the operation of which requires knowledge of aerodynamics, meteorology, navigation, engines and propulsion, electronics, communication protocols, airspace structures, ATC procedures, aircraft certification, human factors, crew resource management, etc.? Politicians? Really? How can a person (or group) who doesn’t understand the system regulate the system?

We need to be regulated by a group who is knowledgeable and who is not tied to the status quo except to the extent that it works, which it sometimes doesn’t. Further, pilots are at the sharp end of the industry. If our passengers (and/or folks on the ground) are in danger, so are we. So we have a clear vested interest in improving operational safety for the benefit of society. This means we have an interest in managing both short-term and long-term risks to enhance operational safety.

Individual pilots almost never have the power to initiate positive change—even if they do recognize the need and the manner in which it can be accomplished. As a group, not only can we make better, more forward-looking decisions, but we would have the power to implement and enforce these decisions.

The bottom line here is that not only are we capable of self-regulation, we (and society) need it. Will there be errors made along the way? Sure. We’re talking here about a system designed and managed by humans. There will be errors. But this doesn’t need to be a deal breaker—the political status quo is certainly no better. The inherent motivation of self-regulated pilots will drive us to identify and correct errors as they happen, or in the short-term afterward. Further, pilots are just one component of the system. Our efforts are augmented by those of Air Traffic Controllers, Maintenance Engineers, Dispatchers, etc. These groups will continue to be regulated independently of pilots—either by Transport Canada in accordance with the current status quo, or through their own self-regulation arrangements.


Happy Flying!

Wednesday, November 3, 2010

Piloting as a Profession: Part 2, Are We Professional?

... Continuing from the last post (Part 1, The CPPC) and considering the question, "Is flying a profession?":

Quoting from other sources, Wikipedia makes the following comments regarding professions:
"A profession is a vocation founded upon specialised educational training, the purpose of which is to supply disinterested counsel and service to others, for a direct and definite compensation, wholly apart from expectation of other business gain."
"A profession arises when any trade or occupation transforms itself through ‘the development of formal qualifications based upon education, apprenticeship, and examinations, the emergence of regulatory bodies with powers to admit and discipline members, and some degree of monopoly rights.’"
The first of these comments applies to pilots. The second is under way in Canada with the College of Pilots. So piloting at least approximates a profession in the formal sense of the word.

There is no legislation in existence that allows pilots to self-regulate. This is one of the key criteria to be a true "profession". So, strictly speaking, we are not a profession. The real question here is: "SHOULD we be a profession?", or perhaps "Are we CAPABLE of being a profession?". So, do we (or can we) meet the criteria of being a profession, and would society benefit from our professional status?

Self-regulation is not the only criterion for a profession, so let’s look at some other important points. Borrowing from some other sources, I’ve come up with the following partial list.
  1. Participation is for Gain or Livelihood.
  2. Activity is Beneficial to Society.
  3. Profession has Legislation to Support Self-Regulation.
  4. Entry into the Profession Requires Significant Educational Achievement.
It’s worth noting that there isn’t a fully clear-cut and accepted definition of a “profession”. So even if I tried to provide a comprehensive listing here, it would inevitably be incomplete and open to debate. This list hits the key points that are, for the most part, universally accepted.

The first criterion, "Participation is for Gain or Livelihood," is easy. Professional pilots operate aircraft for hire. This does, however, call into question the professionalism of those who work for free in order to "get hours". Oh dear. Did I say that out loud? Them’s fightin’ words! Perhaps there’ll be more on that in a future post...

The second criterion,"Activity is Beneficial to Society," isn’t much tougher. Transportation of people and goods is necessary for modern society to exist, and indeed this activity makes up a large portion of the aviation industry. But aircraft are used for far more, and even without the need for transportation, the aviation industry would still be needed by society (albeit on a smaller scale). The list of aircraft activities is extensive. Some activities that come to mind immediately include:
National Defense (which itself includes a whole host of different flight activities), Search and Rescue, Medivac, Law Enforcement, Fire Monitoring and Fighting, Pipeline and Wireline Patrol, Geo Surveying, Research and Development, Weather Observation and Research, Agriculture Support, and so on.
All of these activities benefit society. They, by their very nature, must be conducted by experts who are proficient in the relevant operations, and are knowledgeable about the applicable variables and contingencies. Further, the ability of the operator (i.e. – the pilot) to plan and conduct these activities safely impacts society’s exposure to risk. Such statements could just as easily be made regarding other professions (e.g. – medicine, engineering).

Criterion #3, "Profession has Legislation to Support Self-Regulation," is clearly not met at this time. However, it is worth discussion with regard to the ability of the industry to govern itself (see next post!).

The fourth and final listed criterion, "Entry into the Profession Requires Significant Educational Achievement," is debatable. Transport Canada’s standard for the issuance of a license it really not that high—based more on hours flown than on any real demonstration of high-level skill or knowledge. Certainly, some schools set and enforce a high standard. Some others do not. Some students at these other schools set their own high standard. Some others do not. This inconsistency is something that I hope the College can address—and it is in fact one of the primary purposes of the self-regulation of a profession.

So, back to the original, modified, questions: "SHOULD we be a profession?" or "Are we CAPABLE of being a profession?". The answer is clearly yes. There is work to be done. But everything that needs to be accomplished can be in the near term. The only issue that remains up in the air is that of legislation. Passing new law through parliament is an inherently political process, and is far beyond my expertise. However, I think it’s fair to say that this may be a very time-consuming process. This doesn’t make it any less of a worthy goal, just something we have to be realistic about.


Happy Flying!

Monday, November 1, 2010

Piloting as a Profession: Part 1, The CPPC

A fairly recent development in the Canadian Aviation industry is the new presence of the College of Professional Pilots of Canada. This College is still in the process of getting on their feet, but they’ve already inspired some rather vigorous debate over the state of the industry and, more specifically, the role of "pilot" (for example, HERE and HERE).

According to their Mission Statement, the College’s intention is to operate with Transport Canada through a Safety Partnership Program to “regulate licensed commercial and airline transport pilots and provide and administer guidelines for safety in commercial and airline transport aviation.”

The Mission Statement goes on to say:
The College’s goal is to establish and maintain standards for education, training, certification, aircraft and instrument rating, professional competence and professional conduct of commercial and airline transport pilots. The College’s mission is, with the authority of the Minister, the governance of professional pilots in the interests of public safety and efficient commercial flight activities.

The College’s governance will include the establishment and maintenance of standards for training and professional conduct and the enforcement of such standards.
All of this seems reasonable to me. Having a group run by, and answerable to, those in the industry would appear to be the most effective way to regulate the industry for the benefit of society. This is especially true with regard to training (my own area of expertise). The training philosophy in aviation hasn’t changed appreciably since World War II, despite significant advances in technology and major changes in the nature and demographics of the industry.

Regardless of how reasonable the College’s approach seems, it presents us with at least three questions that will continue to be debated for some time:
Is flying a profession?
Can pilots self-regulate without compromising public safety?
Is the training/education provided to pilots adequate?
I’m inclined to accept the answer to the first two of these questions as “yes”. But that’s a position that needs to be supported since it is not universally accepted, even within the industry itself. As for the third question, the training industry tends to be hot and cold—some schools do a great job, while others do an ... er ... not so great job. This lack of consistency is a serious problem that leads to a whole host of other problems. It needs to be addressed, and is probably the place where the College can have the most positive impact on the industry—at least in the near term.

There are those who disagree with me. Many fear that the College will become "just another union". This intent has been explicitly denied by the current College executive. Nonetheless, it strikes me as a reasonable concern. But the best way to address it appears to be to get involved—and to make sure the College develops into an organization with the whole industry’s best interests in mind. By all appearances, this is indeed the direction that the College is headed in. But, the political process being what it is, it can’t hurt to get involved and have your say.


Happy Flying!

Monday, October 25, 2010

Tubulence Penetration

Several posts ago, I wrote a 2-part piece about Maneuvering Speed—Va in V-speed notation. One of the common misunderstandings about maneuvering speed is that it is a turbulence penetration speed—or, according to some, a maximum turbulence penetration speed—not to be exceeded in gusty or turbulent conditions. As discussed in the posts, Va is used to define the minimum allowable structural strength of the control surfaces. The requirements set for Va make no reference whatsoever to turbulence.

We know, of course, that we do often fly in turbulence, and that turbulence subjects the airframe to structural loads. We also know (or can figure out) that these structural loads will vary with airspeed—they’ll be higher at higher airspeeds and lower at lower airspeeds. So it might be useful to know if there are V-speeds related to turbulence loading, what these speeds are, and what criteria is used to determine these speeds.

As it turns out, there are several speeds at which there is a (direct or indirect) required structural tolerance for turbulence (and Va is not one of them!). Two of these speeds are always published in the flight manual—and marked on the ASI—for normal and utility category aircraft: Normal Operating Speed (Vno), and Never Exceed Speed (Vne). Also related to turbulence, but not always published, are Vb (Gust Penetration Speed), Vc (Design Cruise Speed) and Vd (Design Dive Speed).

The required turbulence tolerance of the airframe is directly defined at three of these speeds, with progressively lower requirements at the progressively higher speeds of Vb, Vc, and Vd. The turbulence requirements for Vno and Vne are indirect since these speeds are defined in terms of other speeds (Vc and Vd, respectively).

Gust Penetration Speed, or Vb, is required to be determined and published for commuter category aircraft, but is usually unpublished for normal and utility category aircraft. Vb is the maximum speed at which the aircraft structure can withstand a 66 foot per second (fps) gust perpendicular to the flight path. How much is 66 fps? It’s about 39 knots, and that’s a helluva gust!

At first glance, 39 knots may seem pretty extreme, but isn’t really when you consider the nature of turbulence. In turbulence, we can encounter two opposing gusts one immediately after another. If these gusts are 20 knots each, the net effect as we transition from one to the other is a 40 knot change. So turbulence that corresponds to a 20 knot gust factor should have us slowing down to (or below) our Gust Penetration Speed, Vb.

Design Cruise Speed, or Vc, is the maximum speed at which the aircraft structure can withstand a 50 fps gust perpendicular to the flight path. At Vc, stronger gusts will overstress the airframe. Above Vc, a 50 fps gust will overstress the airframe. How much is 50 fps? About 29 knots. Using similar reasoning as above, a double gust of 15 knots each can bring us just beyond this limit. So if we’re operating in conditions where the gust factor is at, near, or above 15 knots, we should keep the airspeed below Vc.

How do we do that if Vc isn’t published? Easy peasy! Normal Operating Speed, or Vno, is based on Vc. Vno is usually equal to Vc, but under some conditions it can be lower than Vc. So using Vno as our turbulence limit will be correct, or, in some cases, will err on the side of caution. We can see Vno on the ASI: the top of the green and bottom of the yellow arcs.

It’s generally said that Vno should only be exceeded in very smooth air and even then only with caution. This is fair comment, if for no other reason than we like to have a comfortable margin of safety when it comes to structural failure. Further, even in smooth air, there can be turbulence that we don’t “see” until we’re in it. However, the certification standard does not require perfectly smooth air above Vno. As stated above, the turbulence allowed at Vno is 50 fps (almost 30 knots) perpendicular to the flight path. As we move above Vno, the airframe’s tolerance for gusts is reduced progressively until the lowest requirement (25 fps, or almost 15 knots) is met at Vd. Vd, in turn, is closely related to Vne.

Vne, as all pilots know, is the NEVER EXCEED speed. We never fly at speeds above this for fear of ripping the wings off—quite literally—and then flying much faster and in the manner of a lawn dart, followed by an unpleasant encounter with the ground. This is not hyperbole. Vne is never to be exceeded for several very good reasons (flutter, static divergence, control reversal), which will probably be the subject of a future post. For the moment, let’s have a quick look at the turbulence tolerance required at Vne.

Vne is defined as being no higher than 0.9 times Vd. Vd is where all of the nasty things noted above might happen and the airframe may rip itself apart. The 10% margin is there to allow for manufacturing tolerances and aging of the aircraft, so don’t fool yourself into thinking you can exceed Vne by 10%. The turbulence requirement is applied at Vd, and as such, we can "theoretically" take 10% more gust velocity at Vne. But why push our luck?

At Vd (and therefore at Vne for all practical purposes), the airframe must be able to withstand a gust of 25 fps perpendicular to the flight path. This is almost 15 knots (14.8 knots if you’re picky), which really isn’t very much at all when you account for the double-opposing-gust possibility discussed earlier. Flying in gusty conditions where the gust factor is over 7.5 knots is commonplace. In fact, a gust factor lower than 7.5 knots would barely be noticed in many aircraft bigger than a light 2-seater.

So if we plan on flying at speeds approaching Vne, we definitely want smooth air. This is especially true since Vne does NOT include a tolerance for momentary overspeeding due to airspeed variations in gusts (some speeds, such as the flap limit speed, Vfe, do in fact allow for such momentary overspeeding due to gusts). It’s possible (in truth, not entirely likely, but possible) that during flight at Vne, a gust can introduce catastrophic flutter and prematurely end our career. This alone is a good reason for applying a margin to Vne and avoiding turbulence when flying at very high speeds.

Ok, that’s all well and good, but what about Va? Well, as stated earlier, the standard for Va makes no reference whatsoever to turbulence or gusts. However, there is an argument that in extreme turbulence we may need to use full control authority (read “deflection”) in order to retain control of the aircraft. This is a valid point. However, I hope never to experience it first hand! The best way to deal with this problem is to avoid it. Check your weather, avoid forecast and reported severe turbulence, avoid thunderstorms, and avoid flying near ridges in strong winds. If you have stormscope or weather RADAR, use it. If there are turbulence PIREP’s, pay attention to them. Turbulence that requires regular use of full control authority likely goes beyond any turbulence defined by the certification standards—and beyond the ability of most pilots to maintain positive control for any extended period.

One final note with regard to turbulence PIREP’s. An aircraft’s sensitivity to turbulence is based almost entirely on it’s wing loading (almost because dynamic stability will also play a role). Higher wing loading results in a smoother ride. Lower wing loading results in a wilder ride. So if you’re reading (or listening to) a turbulence PIREP from a heavier aircraft with higher wing loading, interpret accordingly!

So there you have it. A few more tips on V-speeds, where they come from, and how they apply to flight operations.

Happy Flying!

Monday, October 18, 2010

How High Can You Fly?

I was recently reading a thread on an online forum (How high can You Fly? at www.aviationbanter.com).

The question asked by the original poster was basically, “If engine limitations disappear, how high could an aircraft fly, given aerodynamic and airframe limitations?”. Interesting question, I thought. Unfortunately, the thread degenerated into personal sniping and, in many cases, a demonstrated lack of understanding of the problem(s) being discussed. So I thought I’d take a run at the question here.

First of all, engine limitations will never really disappear. That is, unless someone (who will subsequently become very rich) finds a way to circumvent the Second Law of Thermodynamics. However, with enough technological advances, these limitations can become practically insignificant in comparison to other limitations we face. So let’s look at the question from the idealized position of no engine limitations other than the fact that the engine must be air breathing (for combustion or some other chemical reaction) or at least air processing (for a propeller or fan).

The fact is, for currently existing airframes, eliminating engine limitations wouldn’t significantly improve maximum altitudes. It would almost certainly improve cruise and climb performance within the existing altitude range—consider an engine that produces more power from a the same weight, or one that doesn’t lose power as altitude is gained. It might also lead to small improvements in maximum altitude. But big changes in maximum altitude would also require changes to the airframe design.

Two non-engine problems that show up at high altitudes are critical Mach (resulting in the so called "Coffin Corner"), which is due to compressibility effects, and a decrease in the damping of flutter, which is the result of reduced air density.

Critical Mach (Mcrit) is the lowest speed at which a portion of the airflow over the top of a wing travels at or above the speed of sound. As the airflow slows down again, it forms a shock wave, which causes airflow separation—leading to a loss of lift and a massive rise in drag. As a general rule, thinner wings have a higher Mcrit than thicker wings. This is one reason why high altitude aircraft tend to have thinner, more lightly cambered wings.

Mcrit becomes an issue because at higher altitudes, a given indicated airspeed corresponds to a higher true airspeed (due to reduced air density). At the same time, the speed of sound is getting lower (due to reduced air temperature). So for a given indicated airspeed, Mach number gets higher as altitude increases. Conversely, for a given Mach number, indicated airspeed gets lower as altitude increases. This means that Mcrit, which is a fixed function of wing design, corresponds to a progressively lower indicated airspeed as we climb higher.

Sooner or later as we climb, Mcrit enters into the cruise speed range. At some altitude, stall speed and Mcrit meet, and there is no speed at which controlled equilibrium flight can be maintained. No matter how good our engine is, we must remain below this altitude at all times. We must also be cognizant of the narrowing range of useable airspeeds available as we approach this altitude. As an example, the U-2 high altitude spy plane has a tiny speed margin at it’s operational (read “spying”) altitude. 5 knots too slow and it stalls, 5 knots too fast and it overspeeds! Airline pilots, flying aircraft that are designed for high altitudes, must be very aware of the reduced speed range available at higher altitudes. The problem shows up at much lower altitudes in aircraft that are not designed for high Mach number flight.

Airframe problem number 2 is the effect that altitude has on Vne. One of the defining features of flight at speeds over Vne is the presence of flutter, which is an unstable and destructive vibration in the airframe which is aggravated by high speed airflow. This vibration is damped at low altitude in the higher density air. The damping effectively increases the value of Vne. To a first approximation, we can treat Vne as a constant true airspeed v-speed.

So the bottom line here is that the indicated Vne actually drops as altitude increases—it isn’t constant, as we normally assume. Manufacturers account for this in many cases by adding a carefully determined safety factor that allows for reduced damping at the aircraft’s absolute ceiling. Some manufacturers choose instead to publish multiple Vne’s, which are lower at higher altitudes—up to the aircraft’s absolute ceiling. Either of these approaches works fine, but what happens if we strap a new engine onto the airframe and enable flight at higher altitudes? In the absence of additional manufacturer’s Vne data, flying to higher altitudes is a gamble. We could inadvertently exceed the altitude-appropriate Vne and find ourselves in a world of hurt. This problem is easy to fix if we have data on the Vne change with altitude. But we will still eventually run into problems because the margin between Vs and Vne is too narrow—assuming we don’t run into Mcrit problems first!

So all in all, it fair to say that if-and-when far superior engine technology becomes available, airframe design will have to be adapted accordingly. Simply bolting newer and better engines onto existing airframes won’t allow us to realize the full potential of these engines. Alas, this is not a problem we’ll likely need to address for many years yet!

Happy Flying!

Monday, October 11, 2010

Fall Like a Leaf, Grasshopper

Today I went on a "Mutual Proficiency Flight" in the Grob. These flights are used here to keep instructors proficient without the instructor practice being obtained at the expense of the students. It’s an excellent program for several reasons, not the least of which is the fact that we can work on improving our own flying skills without worrying about students seeing us get it wrong. This is not about pride or ego, but about the fact that students are following our example, and if they see us do something wrong, there’s always the risk that that’s the example that will be followed.

One of the exercises we did was a "Falling Leaf Stall". The Falling Leaf is a maneuver in which we enter a stall and, rather than recover immediately (as we usually do), we remain in the stall for an extended period—often losing multiple thousands of feet of altitude. This gives us an opportunity to observe the symptoms of the stall for an extended period and to (try to) keep the wings level with rudder. Most aircraft are directionally unstable in the stall, so directional and roll control can be tricky, and ailerons are usually a no-no (“Why?” You ask? This is a topic for another post!). I wanted to do the Falling Leaf because I’m still very new to the Grob, and I’ve always considered the maneuver to be an excellent skill-building exercise.

Much to my chagrin, I didn’t do a very good job. I guess I didn’t do terrible, but mediocre would be a fair assessment. My training partner, Brandon, did a much better job. So, of course, I had to try a second attempt. It was an improvement, but still not as good as Brandon’s first try. In both of my attempts, I had to recover earlier than planned in order to avoid spinning—which, of course, is one of the points of the exercise!

During normal stall training, we recover from the stall either at the "first indication" (which, in practice, means before the stall), or immediately upon entering the stall. This makes a lot of sense, since the objective is to recover with a minimum loss of altitude. Why is this minimum loss of altitude so important? Stalls in the “real world” generally occur at low altitude. So they mandate a quick and effective recovery to prevent an unpleasant encounter with the ground (which, in case you can’t tell, is a euphemism for “crash”). So it makes sense to train the way we fly. A quick recovery in training will promote a quick recovery in the real world.

The problem with this quick recovery approach is that it limits our exposure to aircraft behavior in and around the stall. Why is this bad? Well, for at least two reasons: 1) The more exposure we have to stall symptoms, the better we are at recognizing an unplanned stall, and 2) Aircraft behavior (read “control response”) in the stall is usually very different than aircraft behavior out of the stall (I say "usually" because different aircraft types have different stall characteristics).

Point (1) is important because in order to recover from an inadvertent stall with minimum loss of altitude, we first have to recognize that we are stalled (or about to stall). Failure to recognize a stalled condition is just as bad as an inability to recover.

Point (2) is important because the vast majority of aircraft types require that we not use ailerons while stalled (and like I said above, this is a whole ’nother post). This is a hard habit to break since at all other times, we control roll with ailerons. Ask a flight instructor how difficult it is to get students to not use ailerons to correct for a wing-drop in a stall and they’ll tell you all about it. But find an instructor who uses the Falling Leaf, and you’ll probably hear a different story. The difference comes down to the oft-quoted mantra of "Practice Makes Perfect" (or, more correctly, "Proper Practice Makes Perfect"). More time spent in the stall, correcting correctly, leads to better directional corrections, even during the quick stalls that we normally train for.

It’s always struck me as odd that the Falling Leaf isn’t a required exercise for the training of pilots. In fact, I’ve met instructors who have never heard of the exercise. If you fly and you’ve never tried the Falling Leaf, go up with an instructor who is familiar with the exercise and try it out. If you’re an instructor and you’ve struggled with your student’s directional control during stall training, try the Falling Leaf exercise and see how things improve.

Happy Flying!

Monday, October 4, 2010

To Be or Not To Be -- An Instructor, That Is

One of the questions that often gets asked by new Commercial Pilots or Commercial Pilot candidates nearing completion is the dreaded, "Should I get my Instructor Rating?". It shows up again and again on online aviation forums (for example: here), and practicing instructors are constantly getting the question from students.

I refer to the question as "dreaded" because there really isn’t a right answer. The answer is different for everyone. Should you or shouldn’t you? Maybe. Maybe not.

I’m inclined to say that if you have no experience beyond your own training, then you shouldn’t be instructing. But that view ignores the present reality of the industry, and I’ll leave it aside for now. Perhaps it will make an interesting future post.

The main question you need to ask yourself is, "Do you want to be a flight instructor?". This shouldn’t be confused with, "Do you want to build hours at someone else’s expense?", which , alas, is a far-too-common motivation for people who don’t actually want to instruct. There are other ways to build hours. If this is what you’re looking for, do some homework and find them. But do your homework early, the direction you choose may influence choices you make during your CPL training (e.g. – do you need float time? taildragger time? multi-engine time? mountain experience?).

So, do you want to be a flight instructor? Think before you answer.

Think about it another way: If your instructing flight hours didn’t count in your logbook, would you still be interested? If your answer is no, that’s a red flag. Perhaps it’s not a show stopper, but it’s definitely a red flag. There are in fact some charter and airline companies that don’t recognize instructing as "real" experience. Frankly, I don’t agree, but again, this is a topic for a future post. But you have to realize that these companies are out there. Of course, there are also charter and airline companies that show a (usually small) preference to ex-instructors—at least partly because they make promising future instructors (i.e. - training captains, company check pilots, and various pilot/manager positions).

The bottom line here is that if you’re just instructing to get hours and move on, it’s a bad idea. Even if you ignore ethical and professional considerations—such as the instructional commitment and quality of instruction received by your students—you will be miserable. Instructing, done right, is hard work. It’s very rewarding for those who have a genuine desire to teach, but it’s tedious and frustrating to those just building hours. Between the classroom, simulator, and administration (i.e. – paperwork), your actual flight time is less than half of your work. Again, this really isn’t a problem for those who want to teach. But if you just want to fly and don’t care so much about the development of others, this can be a painful existence.

So if you want to instruct and believe you will find it rewarding, do it! If not, move on. Get an entry level position towing banners, doing pipeline patrols, or working the dock in anticipation of flying floats (which will require you to get float experience first—do that as part of your CPL!).

Happy Flying!