Aviation Safety Corner
GREETINGS! For this month's topic, I would like to discuss, "Anatomy of an Engine Failure." Examining
the nature of power losses on takeoff and how they can be avoided. This is Part I of IV.
Let's begin our discussion with, "Trend Analysis." We didn't notice it at first, what with the excitement of preparing for a scenic flight, out over the Gulf of Mexico. I was doing my preflight inspection of the Cessna 172, when my brother hollered, "Look! Down there." It was the tail of a Mooney sticking up from the rocks and weeds. We went to investigate.
The airplane wasn't damaged too badly, considering it had skidded with a collapsed gear about a hundred feet across the rocky and brush-strewn terrain. We found out later that the engine had quit late in the takeoff roll and the pilot, trying to figure out what was wrong, had his head down, when it should have been up, and ran off the runway. Fortunately, no one was hurt, and the airplane was trucked out of the strip a few days later for repair.
They were lucky. Roughly 1 out of every reportable accidents involves an engine problem on takeoff, and in about one-third of these cases, the occupants of the aircraft are killed or seriously injured.
To examine how and why this type of mishap occurs, I asked the NTSB for a recent two-year sample of reports on accidents involving power loss on takeoff or initial climb. The sample included 273 accidents, and it was a real eye-opener. An overwhelming number of the cases proved the truth in the old Air Force saying that "accidents are caused and, therefore, preventable." Poor maintenance, cockpit management, operating technique and/or decision-making played roles in many of the accidents.
Right up front, I should mention that the investigators' findings do not support the belief that a power loss on takeoff is most likely to occur at the first power reduction. This happened in only 4 of the 273 accidents. What actually caused these power losses could not be determined, although in one case, the pilot admitted that he hadn't turned on the boost pump, as recommended in his Navion owner's manual, either before or after the engine quit.
We'll consider power reductions in more depth later; but first, let's take a look, in detail, at what leads to accidents involving powerplant failures or malfunctions on takeoff.
Now, Let's Discuss, "Where's the Gas?" In Spite of the warnings throughout our primary training, fuel-related problems appear to play the biggest role. Nearly one-third of the accidents (85 of them) in our sample were caused by fuel contamination, fuel starvation or fuel exhaustion.
Fuel system problems that could be classified as unpreventable, or, at least, not easily identified were involved in 19 other accidents.
Water was the culprit that doused the fires of internal combustion in 18 of the accidents. Sources included water-contaminated fuel trucks and other dispensing tanks (five gallons of water were found in the sump of one such tank following an accident), and wash water and rain that entered through bad seals caps. In only one case did the pilot report that he'd performed a preflight check of the fuel prior to takeoff.
Twelve other accidents were caused by fuel contaminated with some form of foreign matter, such as rust from corroding aircraft fuel tanks and residues of various fuel additives.
In most cases, however, the pilots simply ran their tanks dry. One flew a Cessna 150 three times on training flights without refueling; only unusable fuel was found in the tanks after the crash. In many other cases, very little or no fuel remained. Some accidents occurred when pilots attempted to fly to nearby airports to gas up.
Besides those who exhausted their fuel supplies were several pilots who starved their engines for fuel by positioning the selector valves on empty tanks. Miscellaneous problems relating to fuel lines, fuel pumps and carburetors caused the early termination of several other flights.
In one case, a homebuilt builder/pilot discovered that one does not use automotive-style vinyl fuel hose in proximity to an airplane engine. Another pilot took it upon himself to replace the rubber gasket in his gascolator bowl, only to have it float downstream and clog the line at the carb. The investigation of one accident turned up clogged jet in a brand-new carburetor, apparently the fault of the factory. A few cases of fuel pump failure and/or poor pump operating technique completed the list.
Now in Conclusion, Remember during takeoff, we know a lot about our situation, even when things are going wrong. We know that we're close to the ground, near stall speed, with precious little time to correct a problem and with few options for landing so be prepared and be alert.
Don't miss next month's, Aviation Safety Corner, when we'll continue discussing, "Anatomy of an Engine Failure." Our topic will be, "Blocking the Flow." And "Mechanical Problems." This will be Part II of IV.
Larry G. Harmon
FAA Aviation Safety Counselor