Schweizer 269C N1831A accident near Allentown, Pennsylvania

Probable cause

Inadequate maintenance of the helicopter’s magnetos, which resulted in a partial loss of engine power during the initial climb due to a failure of the left magneto and malfunction of the right magneto.

NTSB analysis

Shortly after takeoff, the pilot of the helicopter transmitted a mayday call over the radio. The helicopter subsequently impacted a building, resulting in substantial damage to the airframe, serious injury to the pilot, and minor injury to the passenger. Neither the pilot nor the passenger provided statements regarding the events that transpired during the flight. Postaccident examination of the airframe and engine revealed no evidence of any preimpact mechanical malfunctions either, with the exception of the engine’s magnetos. Examination of the right magneto revealed evidence of corrosion and indications of misfiring in the distributor block assembly; therefore, it is likely that the right magneto was not performing optimally during the flight. Additionally, examination of the left magneto revealed a worn cam gear, and functional testing indicated that the magneto could not produce adequate spark for engine operation at any power setting.

A review of the helicopter’s maintenance logbooks revealed that the most recent 100-hour inspection was performed about 3 months and 35 flight hours before the accident. The right magneto was installed about 2 years before the accident as a used-serviceable unit, with no previous history or time in service information. The left magneto was installed as a new unit at the same time as the right magneto. There was no indication that the left magneto had been serviced in accordance with the manufacturer’s 500-hour inspection. Given this information, it is likely that the helicopter’s engine at least partially lost power shortly after takeoff, and that the loss of engine power was most likely the result of the failure of the left magneto and the sub-optimal output of the right magneto. Further, it is likely that a lack of adequate maintenance of both magnetos resulted in their degraded performance during the accident flight.

Text from the NTSB. Open the NTSB docket for ERA19LA245 for the full record.