Cirrus Design Corp SR20 N124RR accident near Egg Harbor City, New Jersey

Probable cause

A partial loss of engine power due to the fatigue failure of the alternate air valve, which separated and partially obstructed the engine’s induction system.

NTSB analysis

The pilot reported that while climbing shortly after takeoff, he felt a “kick” to the right side of the plane and the engine began to run rough, followed by a partial loss of power. The pilot was unable to maintain altitude, so he turned back toward the departure airport. He determined he was not going to be able to reach the airport and as he lined up for an off airport forced landing, the engine regained full power. He turned back toward the departure airport and initiated a climb, but after about 30 seconds the engine power reduced a second time and remained at partial power. With no suitable landing area, the pilot activated the airframe parachute system. The airplane descended under canopy, coming to rest in a wooded area and resulting in substantial damage to the airframe.

Recorded engine and performance data from the flight were consistent with a partial loss of engine power and corresponding fluctuations in fuel flow and rpm in the minutes preceding the accident. A postaccident test run of the engine was successfully completed, though some engine roughness, backfires and brief puffs of white smoke were observed. After running for several minutes, the engine began to operate smoothly and normally. Detailed postaccident examination of the engine and its constituent components revealed that half of the alternate air valve was unattached and was loose inside the engine induction housing assembly. The opposing half remained partially installed on its respective mount/actuator inside the induction tube. Based on the available information, it is likely that when the valve failed, it separated and was pulled into the induction housing, partially obstructing induction airflow and disrupting the engine’s fuel/air mixture. The inconsistent loss and subsequent gain of power that occurred during the accident flight was likely attributable to the valve shifting inside the induction housing.

Metallurgical examination of the fractured rivets that held the valve assembly together revealed fatigue fracture signatures alongside small areas of ductile dimples consistent with final overstress failure. No evidence of a preexisting induction system issue was documented in the airplane’s maintenance records and the airframe manufacturer reported that no similar failures in other airplanes had been previously documented.

Text from the NTSB. Open the NTSB docket for ERA24LA333 for the full record.