2012-08-We-Dont-Know-What-We-Dont-Know

34 AUGUST 2012

Here’s a question for both “seasoned” and relatively new or low pilots. While on a cross-country flight en route to a fly-in, you encounter a problem: The engine begins running a bit rough, the tachometer is showing a 500 rpm fluctuation, and oil pressure and temp both seem to be normal. There is an airport 15 miles ahead, another 12 miles behind you, and a shorter turf run-way airport just 2 miles to the right of your flight path. You’ve been cruising at an altitude 3,500 feet above the reasonably level but unfamiliar terrain. What would you do? Why?

This question and similar others are now part of the new FAA Practical Test Standards required to be used by FAA and Designated Flight Examiners alike, as of June 1, 2012. In addition to being able to demonstrate normal flight maneuvers, student applicants are now required to analyze and respond correctly to scenario-based situa-tions while in flight.

The FAA theory behind scenario-based training is to better prepare a student for possible real-life flight situ-ations. So, we instructors are now required to teach sce-nario-based situational flight challenges.

With little or no practice, how many of you seasoned as well as low-time pilots could take and pass today’s sport or private pilot scenario-based checkride?

Sitting in an easy chair enjoying a cold refreshment at day’s end and thinking about flying (isn’t that what all of us do who have been struck by the flying gods?), it is fairly easy to analyze the situation presented above and draw a conclusion as to how we would handle the prob-lem. But put yourself in the airplane in real time and now what would you do?

Do you continue to the airport ahead? Do you make a 180 and fly to the closer airport behind you? Do you pick the shorter turf runway 2 miles away? What things might you consider in making that decision?

Prior to departure, did you check the METARs for actual and forecast surface winds along your route of flight? How about the forecast winds aloft for the area? These factors will all come into play in arriving at a sound plan of action. You might be dealing with a 10- to 12-knot head wind slowing your groundspeed. Think

about it for a moment. Do you know the glide ratio of your airplane? How far can your airplane fly or rather what is the rate of descent on partial power? No power? You’ve got 3,500 feet of altitude to work with, an indi-cated glide speed of 75 mph, but due to the head wind, the groundspeed is 65 mph. Can you make the airport 15 miles ahead of you?

What if you opt to turn around and take up a head-ing to the airport 12 miles behind you? Can you make it to that airport now that you’d have an 85 mph ground-speed and a dozen miles to cover before using up every foot of that precious 3,500 feet of altitude? That is assum-ing the engine continues to run providing partial power.

Many of us would probably make the wrong decision initially, causing a greater problem. That decision would be to start changing the throttle setting. When is a “sick” engine most likely to fail? When power adjustments are inputted! The worst thing one could do is change the throttle setting on a “sick” engine, as it can lead to a com-plete engine failure. If the problem truly is the engine, trying to save it by throttling back won’t do any good. It is already turning to junk, so use what is left of it to safely get you to a safe landing site.

The very first thing to remember is always have an out for any in-flight situation encountered. In this case, it is strongly recommended that turning toward and flying to the turf runway 2 miles away is the first step in dealing with this problem. At least then we have the option of landing on a runway rather than a farm field, or worse. Many of us might forget to fly to the nearest runway and begin fumbling with the throttle. Then the engine quits and several minutes have been wasted, causing the loss of perhaps a thousand feet of precious altitude, which further adds to the problem.

After turning to and flying toward the nearby air-port, ensuring it can be reached even without power, then and only then should one begin checking off your engine options.

Editor’s Note: There are always exceptions to most every rule, cardinal or otherwise, so for the sake of this example I’ll stick with the basics.

BY Steve Krog, CFI

THE Vintage Instructor

We don’t know, what we don’t know

After deciding the turf airport can be reached, make sure that the fuel selector is on the proper tank. The rough-running engine may simply be due to fuel surges caused by inadvertently running a fuel tank near bone-dry empty. A few ounces of what is left of the fuel may be entering the fuel line from the tank each time a thermal causes the wings to rock. Switch fuel tanks and give the new fuel supply a few seconds to flow.

Next, apply carburetor heat and see what effect it has on the engine roughness. You may have acquired a good batch of carburetor ice; yes, even on a 75 to 85ºF sunny day, carb ice can cause a problem. Does carb heat applica-tion have any effect on the engine?

If a severe case of carb ice is encountered and carb heat is applied, the engine may run better for a couple of seconds, followed by the sickening sound of it not run-ning. Immediately turn off the carb heat. The heat drawn from the carb heat shroud caused a good bit of the ice to thaw, allowing the water to be sucked into the carbure-tor. The engine will sound like it has quit. Closing off the carb heat allows fuel to flow again, even though it may be somewhat restricted. The engine will cough back to life but may continue running rough. Repeat this process as many times as is necessary until all of the carb ice has been melted.

I have personally encountered this situation a number of times when flying behind a Continental O-200 en-gine. For some reason this engine seems quite prone to carb icing.

For the sake of our scenario-based training, let us as-sume the problem was not carb ice and the engine con-tinues running rough. Proceeding toward the turf runway airport, the next items to check are the magnetos. Simply turn the mag switch from “Both” to “Left.” Does it make any difference? Then turn the mag switch to the “Right” position and see if it makes a difference. By conducting this test we can isolate each magneto to determine if one or the other is causing the problem. If, when switch-ing to the “Right” magneto, the engine began running smoothly, the cause of the problem has been determined and isolated. Continue on to your approach and landing on the good magneto.

If fuel, carb heat, and magnetos have been eliminated as the culprit, continue to the turf runway airport. In do-ing so, however, always plan for the worst, which in this case is that the engine could quit at any given instant.

The recommended manner in approaching the air-port and runway has also changed somewhat under this scenario-based training. It is recommended that the power setting remain as is. To get rid of excess altitude, use flaps if your airspeed is in the safe operating range for extending flaps. Otherwise use a slip to accomplish the same. Only when you know that you can safely slow the airplane and still make the field should power be ad-justed, as the engine may quit the moment power is re-duced. Pick an aim point on the runway approximately one-third of the way down the intended runway. It is al-

ways better and less damaging to you and your aircraft to land long and roll off the end into the grass than it is to come up 50 feet short of the approach end of the runway. Again, common sense coupled with experience in your airplane will dictate the approach.

I would suggest to all pilots, especially those who fly for the sheer pleasure of flight, that you learn all you can about the airplane you are flying. Many of the vintage airplanes we fly do not have published data for best glide speed, etc. Start by climbing to an alti-tude that you normally cruise at, for example 3,500 feet above ground level. Set your power for normal cruise; 2300 rpm is common. Then reduce your power to about 1700 rpm to simulate a partial power loss. Establish the best glide speed and time your descent to lose 2,500 feet. If the best glide speed is unknown, use your usual final approach speed plus 5 to 10 mph. Measure the distance you have traveled while making the descent. Most everyone today has a portable GPS unit that will be handy for measuring the distance. With these known values, one can then easily calculate the rate of descent experienced.

Next, repeat the exercise, but this time reduce the power to idle and compare the time and distance to that recorded from the first trial run. Record and keep these numbers readily available. They may prevent you from having to make an off-field landing someday.

VINTAGE AIRPLANE 35