Proficient Pilot: Partial power

One of the most common emergency procedures taught to pilots involves coping with an engine failure— a total engine failure. According to the Civil Aviation Authority of New Zealand, however, partial engine failures occur three times more often. What makes this statistic so fascinating is that we seldom discuss or train for the possibility of a partial loss of power. Perhaps this is because such an event is regarded as less of a problem than a total engine failure, a possibly erroneous conclusion. (A partial engine failure occurs when an engine produces noticeably less than the maximum power that would ordinarily be available during otherwise normal circumstances.)

A partial power failure can be more challenging than a total engine failure because resolving such a problem is not as straightforward. When an engine fails completely, the pilot of a single-engine airplane is left with few options. He must lower the nose, establish a normal glide, descend, and locate a safe haven upon which to make an emergency landing.

In the case of a partial engine failure a pilot has additional options. Decisions have to be made. For example, a pilot might believe that the engine is developing sufficient power for him to continue to some intermediate or distant airport. This can be an inadvisable plan of action because whatever caused the initial and partial power loss could soon result in a total power loss.

A pilot experiencing partial power failure might be best advised to assume that his engine has or will soon fail completely and regard the emergency as a total power failure. There are exceptions to this, of course. One is that continuing the flight with available power might be acceptable if this progressively improves the likelihood of a safe outcome, such as when overflying progressively improving terrain upon which to make a precautionary or emergency landing. Another exception might be when a pilot knows exactly what caused the loss of power, and he can be certain that further loss is unlikely. I am not keen about such an exception and would prefer instead to abide by that marvelous piece of aeronautical wisdom, “I’d rather be down here wishing I were up there than up there wishing I were down here.” (Does anybody know where this magnificent piece of flying folklore originated?)

A noteworthy example of an accident resulting from a partial engine failure occurred on June 10, 2010, when two pilots—one was a professional, 5,000-hour instructor—experienced a partial loss of power while operating their Piper Malibu at an altitude of 15,000 feet and overhead an air-carrier airport with a 12,000-foot runway. Weather at the Ontario International Airport consisted of a 3,700-foot ceiling and a visibility of 10 miles. The broken cloud layer was approximately 3,000 feet thick, but conditions above the clouds were severely clear. Both pilots had instrument ratings, and the aircraft was equipped with a pair of panel-mounted moving-map displays.

I have presented the circumstances of this flight at safety seminars and asked pilots in attendance how they would have handled the problem. Most said that they would have used their moving-map displays to circle the airport and remain at all times within gliding distance of the two-mile-long runway, a plan of action with which one can hardly disagree. This, however, is not what the pilots of this airplane did. They instead assumed that the engine would continue to deliver some power and allowed themselves to be radar vectored beyond gliding distance of the airport. Ultimately, the engine failed to deliver any power at all, resulting in an off-airport crash, bodily injury, and a totaled airplane.

Think about this for a moment. If the engine had failed suddenly and completely from the get-go (when 15,000 feet over a 12,000-foot runway), it is less likely that this accident would have occurred. The decision to remain within gliding distance of the airport would have been obvious. There would not have been other possible courses of action to cloud the issue. In other words, regarding a partial engine failure as a total engine failure simplifies the decision-making process.

If some power continues to remain available, consider it a blessing, use it if necessary, but do not rely on it remaining available.

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Last month, I cited Leonardo da Vinci’s beautiful prose: “Once you have tasted flight, you will forever walk the Earth with your eyes turned skyward, for there you have been, and there you will always long to return.” I wondered how it was possible for someone who obviously had never taken to wing to be so exquisitely expressive about flight. I wonder no more. Contrary to popular belief, da Vinci did not write that. Credit apparently goes to Henry van Dyke, an American poet.

Barry Schiff is a former TWA captain with more than 28,000 flight hours.

Web: www.barryschiff.com