CHAPTER 4 - SIMULATED ENGINE FAILURES

[Sample Chapter from Flying Wisdom, The Proficient Pilot, Volume 3]

An important part of every pilot's training involves preparing for a variety of emergencies. These include electrical malfunctions, cabin fires, landing with a flat tire, instrument failures, and so forth. Not surprisingly, more emphasis is placed on engine failure than on any other type of emergency. Unfortunately, the simulation of power failure leads occasionally to an actual emergency for which neither student nor instructor is prepared.

Consider, for example, the instructor who chopped the power of her Citabria 7GCAA and challenged her student to make a power-off approach to a forced landing. When the aircraft was 500 feet agl, the instructor declared that the student had failed the exercise because he was not within gliding range of the selected field.

"Whaddya mean?" the student replied indignantly. "I can make that field."

So instead of adding power while at a safe altitude and climbing to an even safer one, the instructor allowed her student to continue. She apparently needed to prove to him that the aircraft was too low to glide to a safe landing.

But the instructor allowed the situation to go too far. When she finally advanced the throttle at 100 feet agl, the engine did not respond because it had failed during the prolonged glide. The aircraft settled into a ditch and was damaged beyond repair. Neither occupant was seriously injured.

FAA records indicate that there were 43 accidents involving simulated emergencies during the past five years. The most common causes were (1) improper use of systems and controls, (2) loss of control, (3) inadequate student supervision, (4) collision with an object or terrain, (5) poor judgment, and (6) loss of power.

An analysis of these training accidents by the Aviation Safety Institute of Worthington, Ohio, indicates that almost all were avoidable. The majority involved experienced instructors in airworthy aircraft, and five involved air carriers. Also, most of these accidents occurred while simulating powerplant failure in single- and multiengine aircraft.

Although the accident causes listed above are apparently correct, they fail to describe what really went wrong. One can say, for example, that an accident occurred simply because a pilot lost control. But to learn from the mistakes of others, we need to know why they lost control.

A study of the accident reports (as well as some reading between the lines) reveals that most accidents related to simulated engine failure occur when an instructor misjudges his ability, his student's ability, or the performance capability of the aircraft.

Another common factor is that instructors often conduct the simulation at a time when an actual failure could not be tolerated. This is one reason, for example, why both the FAA and the aircraft manufacturers strongly discourage simulating an engine failure in a light, piston-powered twin immediately after liftoff. (Multiengine instructors used to "fail" engines during initial climb, but this practice seemed almost as lethal as it was educational.)

Instructors also need to establish rules of conduct before departure. These help the student to recognize whether the emergency is actual or simulated and eliminates dangerous confusion. The instructor might say, for example, that he will not simulate an engine failure below 2,000 feet agl and that any such indication of a failure should be regarded as a genuine emergency.

The two pilots also should determine before departure who is to be the pilot in command and responsible for managing any actual emergency that might occur. The failure to establish such an understanding has led to a number of accidents.

The method used to simulate an engine failure is somewhat controversial. An instructor has four choices. He can (1) close the throttle, (2) lean the mixture to idle cutoff, (3) turn off the magnetos, or (4) turn off the fuel supply. Which of these methods would you recommend?

As far as the engine is concerned, it is best to lean the mixture to idle cutoff while leaving the throttle open. This is because an open throttle permits the cylinders to fill with air and cushion engine deceleration, which reduces internal stresses during the simulation of a sudden engine failure.

Pulling the mixture control, however, actually shuts down the engine. Although this may be perfectly acceptable to the pistons, crankshaft counterweights, and other engine parts, it may not be in the best interest of those on board the aircraft. This is because the engine might not restart on demand, and the practice approach to a forced landing would suddenly become a genuine low-altitude emergency.

A practice power-off approach to a farmer's field usually is terminated by a full-power climb to a safe altitude. But if the engine has been genuinely shut down during descent, it will become quite cool. A quick restart and the application of full power at such a time is unhealthy for any engine. (Powerplant manufacturers also caution against conducting simulated engine failures during extremely cold weather because of the additional wear and tear this might create.)

For similar reasons, neither the magnetos nor the fuel-selector valve should be used to simulate an engine failure. (Turning off the fuel supply to fuel-injected engines is particularly hazardous because these engines can be difficult to restart following fuel starvation.)

Experts at both Teledyne Continental Motors and Textron Lycoming agree, therefore, that closing the throttle is the best way to simulate an engine failure in single-engine aircraft. (Simulating engine failure in a twin will be discussed later).

During prolonged glides, be certain to "clear" the engine by applying power every 30 to 45 seconds. Many pilots believe that this prevents the spark plugs from fouling, but "clearing" usually does not do that because the power application is too short. The most important reason for applying occasional power is simply to confirm that the engine is still running. After all, an idling engine and a windmilling propeller are almost indistinguishable.

If an engine does fail during a prolonged glide, it is best to determine this at a relatively high altitude. A pilot cannot afford to wait until power is genuinely needed to discover that it is unavailable.

Applying power periodically during power-off descents also helps to keep the engine warm and provides a modicum of carburetor heat. (Carburetor ice can form during prolonged idling even when carburetor heat is applied because there often is not enough heat being generated by an idling engine to prevent ice from forming.)

During prolonged idling, fuel can condense and form small puddles in the induction lines of some carbureted engines, especially those using autogas. Adding power periodically also clears out this fuel before it can accrue sufficiently to cause the engine to falter.

When "clearing" the engine during a glide, do not jab the throttle or apply a large amount of power. Instead, move it gently, especially when operating engines with counterweighted crankshafts.

Although closing the throttle may be the best way to simulate an engine failure in a single-engine aircraft, this does not necessarily apply to twins. One reason is that a closed throttle signals to a student which engine has been failed. He is deprived of having to determine which engine failed and then confirming his discovery by retarding the appropriate throttle.

The preferred technique is to "fail" an engine using its mixture control. I usually make it a practice to hide the mixture controls from the student with a large piece of cardboard or a manila folder. In this way, he cannot determine which engine has failed by glancing at the mixture-control levers. This technique gives the student access to the throttles and propeller-pitch controls, and he is forced to go through the procedures just as if the engine had genuinely failed.

Once the student identifies the dead engine and retards the correct throttle, he then calls for "zero thrust," which simulates feathering the propeller. At this time--and with the throttle already retarded by the student--the instructor advances the mixture control, which restarts the engine. He then advances the throttle slightly, just enough so that the propeller produces as much thrust as it does drag (which explains why such a zero-thrust power setting closely simulates the effects of a feathered propeller).

This procedure incorporates the best of both worlds: using the mixture control to cushion the effects of engine shutdown and using the throttle to subsequently keep the engine running smoothly.

Simulating the failure of a turbocharged engine in either a single or a twin introduces the problem of shock cooling. This occurs when an engine operating at relatively warm temperatures is subjected to the rapid cooling that results from sudden power reduction. Although this can be tolerated on occasion without harmful effects, doing so frequently can cause cracked cylinders and other damaging effects. This explains why training aircraft ordinarily are not equipped with turbochargers. (Powerplant engineers concede that some normally aspirated, or nonturbocharged, engines also can be subjected to the long-term effects of shock cooling, but not to the extent of turbocharged engines.)

Finally, it might be interesting to discuss shutting down an engine at the end of a flight. Is there anything wrong with simply turning off the ignition? After all, this is how we turn off automobile engines.

According to powerplant engineers, there is absolutely nothing wrong with turning off the magnetos to shut down an engine. The practice of using the mixture control is to protect people, not engines. When an engine is shut down by turning off the ignition, some fuel remains in one or more cylinders. Someone moving the propeller at such a time (and while the engine is still hot) could cause one or more cylinders to fire and wind up losing a limb in the process. Shutting down the engine with the mixture control reduces this possibility by starving the cylinders of fuel. In any event, a stationary propeller must always be regarded as a potential weapon.