WPR17LA197 · Boeing A75N1(PT17) UNDESIGNAT

The commercial pilot departed on a sightseeing flight with a passenger onboard; the airplane was near its published gross weight. The pilot had experienced some difficulty starting the engine before takeoff, which he resolved after removing and reinstalling the primer several times. The takeoff roll and departure were uneventful; however, when the airplane transitioned to initial climb, its climb performance reduced, and when it reached about 500 ft mean sea level, the airplane stopped climbing, which the pilot reported that he believed was due to a partial loss of engine power. Subsequently, the pilot turned the airplane back toward the departure airport, but after realizing that it would not reach the airport, he chose to conduct an off-airport forced landing. The airplane touched down in a dry riverbed, and it impacted brush and then nosed over and came to rest inverted, which resulted in substantial damage to the upper and lower wings.

The airplane had sufficient fuel for the accident flight. Postaccident examination of the engine revealed numerous preimpact anomalies, including a leak in the engine primer line, which had developed over time due to its repetitive contact with the engine exhaust adjacent to it. The leak likely resulted in the pilot needing to add an excessive number of primer shots to start the engine before departure and led to some of his failed engine start attempts. Further, examination of the engine revealed that the cold compression on the No. 3 cylinder was low, that a spark plug was defective, that two ignition cables had significantly low insulation resistance, and that several of the forward ignition harness elbows were bent. Low compression is not an isolated incident, and it is possible that the pilot had been operating the airplane with low cold compression on the No. 3 cylinder for some time; therefore, it could not be determined if this contributed to the power loss. Although a defective spark plug could have resulted in a negligible power loss, it likely would not have prevented the airplane from climbing during the accident flight. Further, it could not be determined if the ignition harnesses were bent during the impact sequence; therefore, it could not be determined whether the condition of the ignition system contributed to the loss of engine power.

Although the atmospheric conditions at the time of the accident were conducive to the accumulation of serious icing at glide power, it could not be determined if carburetor ice had formed while the airplane was idling on the ground. The reason for the loss of engine power could not be determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset