ERA18LA214

The private pilot of a motor glider was taking off when he noticed the engine sounded "a little rough"; as he turned downwind, he started to smell smoke. He reported that he shut down the engine and returned for an uneventful landing. When the motor glider stopped, the pilot noticed flames below the right door; the flames grew and eventually consumed and destroyed the airplane. Postaccident examination of the wreckage revealed that the exhaust manifold had various cracks on the tubing. Examination of the exhaust manifold revealed the fracture and cracking of the exhaust system manifold tubes was due to fatigue. The fatigue cracks on the exhaust manifold were progressive in nature and had likely been present for some time before the accident, allowing exhaust gasses to begin escaping into the engine compartment before reaching the muffler assembly. It is likely that the exhaust gases caused a flammable condition the that resulted in a ground fire after landing.

On August 12, 2018, about 0840 eastern daylight time, Pipistral Sinus 912, N467L, was destroyed when it was involved in an accident near West Palm Beach, Florida. The private pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot of the motor glider, after dropping off a passenger from a previous flight, he restarted the engine and taxied out to runway 27R. After checking his instrument gauges, he made a radio call indicating that he would remain in the traffic pattern. During takeoff, he noticed the engine sounded "a little rough," and as he turned downwind, he started to smell smoke. He shut down the engine and returned for landing. The landing was uneventful, but when the aircraft stopped, the pilot noticed flames below the right door. After he exited the airplane, the flames grew and eventually consumed the airplane. Postaccident examination of the airplane’s engine by a Federal Aviation Administration inspector revealed that the cockpit was consumed by the fire. Examination of the motor glider's engine revealed that the exhaust manifold was cracked. Further examination of the exhaust manifold by the NTSB Materials Laboratory revealed the fracture and cracking of the exhaust manifold tubes was due to fatigue. In each manifold tube that failed, the fatigue cracking initiated on the inner surface near circumferential welds and propagated through to the outer surface, indicating that the fatigue cracks were likely present before the accident. The fatigue cracking at the fitting led to complete fracture, whereas the cracking in the opposite tube elbow had progressed only part way.