Page 38 - Twin & Turbine May 2017

Twin Proficiency
by Thomas P. Turner A Decision of
Convenience
What effect does a tailwind have on your takeoff performance? More than you might think.
The National Transportation Safety Board (NTSB) released an unusually detailed Preliminary Report on the crash of a turbocharged piston airplane:
The aircraft impacted terrain shortly after takeoff from Stevensville Airport (32S), Stevensville, Montana. The private pilot and his passenger received minor injuries. Visual meteorological conditions prevailed. According to the pilot, he based the airplane at 32S, and he and his wife planned a final destination of New Orleans. The takeoff was conducted from Runway 12.
The pilot “accelerated” the airplane to “80” \[knots\] and then lifted off. Shortly after, the airplane “couldn’t climb or accelerate.” The pilot stated that he was unaware of the cause of the problem, and that it felt like there was a “rapid decrease in power.” He reported that he ensured that the engine controls were in their appropriate positions for full takeoff power, but that the airplane “would not lift” any further. The pilot reported that he had insufficient time to scan the engine power instruments or diagnose the problem, due to the airplane’s proximity to the ground. The pilot did not retract the landing gear during the event. He did not report his maximum altitude, but he did report that he had previously experienced problems with the turbocharger system.
The airplane struck level terrain adjoining the south side of the runway. The airplane came to rest upright about 300 feet from the runway centerline, approximately 3,500 feet along the runway from the Runway 12 threshold end, or about 300 feet prior to the Runway 30 threshold end.
A pilot-rated eyewitness who was situated on the northeast side of the runway, about 2,400 feet from the 12 end, reported that the engine sounded normal. The airplane just broke ground as it passed abeam of him, and he then mentioned to a person who was with him to watch the airplane, because its takeoff appeared to be
unusual. The airplane achieved a maximum altitude of about 50 feet above the ground, and then began a “steep right descending turn.” The right wingtip struck the ground first; it exhibited a brief flash of fire which quickly disappeared. The witness stated that runway 12 has a “substantial” uphill slope, and the terrain and trees also rise in that direction. He also reported that at the time, there was a “quartering tailwind” from the “northwest” of about 15 knots. The 32S automated weather observations were recorded as being from 340 and 350 degrees, between 9 and 12 knots, with numerous gusts to 16 knots. The observations also reported visibility 10 miles, temperature 2 degrees C, dew point minus 6 degrees C, and an altimeter setting of 29.98 inches of mercury.
I call this event and others like them a “crash of convenience.” Of course, there is nothing convenient about crashing an airplane. What I mean is that attempting takeoff uphill with a
36 • TWIN & TURBINE
May 2017