Piper PA 28R-201 N3783M accident near Northampton, Massachusetts

Probable cause

The failure of the alternate air valve plate hinge pin, which caused the alternate air valve plate to lodge in the fuel servo assembly, which resulted in a restriction of air to the fuel servo assembly, a loss of engine power, and an off-airport emergency landing.

NTSB analysis

The flight instructor indicated that, during a simulated soft-field takeoff on an instructional flight, the airplane's climb performance noticeably deteriorated. As the airplane reached about 150 ft above ground level, the engine started to lose power. The flight instructor chose to make an emergency off-airport landing, during which the right wing and firewall were substantially damaged. A postaccident examination of the airplane revealed that the alternate air valve plate was lodged in the air intake and blocked the fuel servo. Further examination revealed that the hinge pin that held the alternate air valve plate was worn completely through, which caused the plate assembly to separate from its mounting location and lodge in the fuel servo. This obstruction likely restricted the intake air to the engine and thus led to the loss of engine power on takeoff. Examination of the alternate air valve plate revealed that it had been altered from its original design, although there were no maintenance records documenting the alteration. The investigation could not determine whether this alteration contributed to the failure of the alternate air valve plate's mounting mechanism.

Text from the NTSB. Open the NTSB docket for ERA16LA280 for the full record.