Flying Lessons - 090319

©2009 Mastery Flight Training, Inc. All rights reserved.

FFLLYYIINNGG LLEESSSSOONNSS for March 19, 2009

suggested by this week’s aircraft mishap reports FLYING LESSONS uses the past week’s mishap reports as the jumping-off point to consider what might have contributed to accidents, so you can make better decisions if you face similar circumstances. In almost all cases design characteristics of a specific make and model airplane have little direct bearing on the possible causes of aircraft accidents, so apply these FLYING LESSONS to any airplane you fly. Verify all technical information before applying it to your aircraft or operation, with manufacturers’ data and recommendations taking precedence.

FLYING LESSONS is an independent product of MASTERY FLIGHT TRAINING, INC. www.thomaspturner.net This week’s lessons:

As we began discussing last week, keeping the airplane on the runway during takeoff and especially landing continues to be a challenging prospect for many pilots, according to mishaps reports and contacts in the insurance industry. Runway directional control is a function of controlling the effects of:

1. Wind

2. Runway surface

3. Dynamic aircraft forces (propeller tendencies, tail design, tailwheel, wing loading, etc) 4. Aircraft malfunctions (tires, brakes, engines, controls) Last week we reviewed some issues related to crosswind landings. This week we move on to the directional control effect of runway surfaces.

Smooth, flat runways at first seem optimal for directional control. In practice, however, a completely smooth surface presents little resistance to movement. If the pilot permits the airplane to drift sideways for any other reason, the completely smooth runway will not resist the excursion. Tailwheel pilots know it’s easier to take off and land on grass runways. Tricycle to tailwheel, grass surfaces provide more friction, and consequently more resistance to directional deviations. It takes more wind (or poorer piloting) to go off a grass runway than a paved one, all else being equal.

If winds are near your personal crosswind limits and fuel is critical, perhaps a nearby turf airport is a better option for landing than the home ‘drome or your original, paved destination.

Runway contamination can contribute to loss of directional control. Puddles of rain “grab” at wheels, imparting forces that can alter the airplane’s directional path. Slush or snow patches are even worse. A coating of ice makes a runway virtually unusable in a crosswind; don’t mix icy runways and anything more than a very slight off-heading breeze. Muddy or wet grass often provides no braking resistance at all; wheels can lock up with braking and the airplane loose all directional control when speed decays below that where flight controls are effective.

According to the National Aeronautics and Space Administration (NASA), hydroplaning occurs when a thin film of water builds between a tire and surface, and actually lifts the tire from the runway. Tires are no longer in contact with the ground; braking looses its effectiveness, and you may not be able to steer the airplane at slow speeds.

Research shows that hydroplaning can occur in as little as one-tenth inch of water. NASA identifies the hydroplaning critical speed as nine times the square root of the tire pressure. This means most light airplanes can hydroplane at as low as 50 knots. Here’s a table of NASA-computed critical hydroplaning speeds:

Tire Hydroplaning

Pressure

(psi) Speed (kts)

30 49

40 57

50 64

60 70

70 75

80 81

Critical Hydroplaning Speeds (source: NASA) Notice that common airplane tire pressure specifications are such that typical landing speeds are at or near the critical level. Compare your airplane’s main tire pressure and the airplane’s stall speed (which you should approximate at touchdown) to see if the aircraft you fly is susceptible to hydroplaning on wet runways.

Aviation legend Sparky Imeson provides this guidance for avoiding hydroplaning on wet runways:

And of course runway width is another factor not in directional control itself, but how much an airplane is allowed to drift off centerline before it becomes a potential safety factor. Most pilots these days are used to runways 75 to 100 feet or more in width, with pilots at more rural airports used to narrower runways, often around 50 feet wide. It’s not terribly uncommon, however, for smaller airports to have runways as narrow as 35 feet. Consider the wingspan of many airplanes approaches (or surpasses) this figure and you can see the extreme need for centerline alignment and directional control.

The primary FLYING LESSON is that we have to choose our landing surface in concert with winds. Don’t let the pilot attitude of resignation make you “give it a try” because you feel you have no other option. Delay takeoff until conditions improve, or divert to another airport if already airborne. Be pilot-in-command and make a decision based on actual conditions and an honest evaluation of your own abilities as well as those of the aircraft. Next week: How features of airplane design affect runway directional control.

Debrief: Readers comment on recent FLYING LESSONS:

Last week FLYING LESSONS asked your opinion on draining fuel tanks completely dry in flight as a fuel management strategy, leaving, of course, adequate fuel in the final main tank for landing and diversion if necessary. As expected, the responses were split almost evenly, with only slightly more readers (about 55%) in favor of draining tanks completely dry, as opposed to burning fuel until tanks were almost dry but not quite causing the engine to sputter from incipient fuel starvation-which Mastery Flight Training, Inc.’s research indicates may be a factor in several fuel mishaps, when the engine will not restart when a fueled tank is selected before the airplane impacts the ground.

Many readers replied with a simple “yes” or “no”, with the “yes” (running tanks dry) tending to be more detailed in their response. Selected reader comments:

In favor of draining tanks dry:

Opposed to draining tanks completely dry:

FLYING Magazine author Richard Collins wrote many years ago, “The problem with most general aviation pilots is not that they have bad procedures, it’s that they have no procedure at all.” Whether you like to burn a tank completely dry or not, do it intentionally, with forethought and planning. Don’t allow yourself to be surprised by the sputter of an engine or a blank engine monitor.

As I’ve stated before, based on mishap history intentionally running a fuel tank dry in flight to the point of incipient engine failure (the engine sputters) is an unnecessary risk and at best is very passenger-unfriendly. If you are extending range to the point you need every gallon of fuel in almost every tank, you need to re-think you risk management strategy—and likely need a longerrange airplane, or to alter your techniques to extend the unrefueled range of the one you’re flying. But that’s just my opinion. What’s yours? If you’ve not already responded, send me your thoughts at mastery.flight.training@cox.net.

Thanks to all those readers who have helped us thoughtfully consider the way we choose to fly our aircraft.

Questions? Comments? Send your insights to mastery.flight.training@cox.net Fly safe, and have fun!

Thomas P. Turner, M.S. Aviation Safety, MCFI

2008 FAA Central Region CFI of the Year

FLYING LESSONS is ©2009 Mastery Flight Training, Inc. Copyright holder provides permission for FLYING LESSONS to be posted on FAASafety.gov. For more information see www.thomaspturner.net , or contact mastery.flight.training@cox.net or your FAASTeam representative.