Two Power-Loss Events, One Unresolved Engine Problem

The first failure was a warning

After takeoff, the aircraft suffered a partial loss of engine power and returned to the airport. A mechanic inspected the aircraft and conducted an engine test run. No anomaly was found during that check, but the reason for the original power loss had not been established. Despite that unresolved question, the pilot decided to fly again and the mechanic accompanied the flight.

Power disappeared again after takeoff

During the second departure the engine became rough while the airplane was climbing through roughly 400 to 500 feet above ground level. The pilot began turning back toward the airport. The engine then lost total power and the airplane struck terrain and obstacles. The short interval between the second power loss and the impact left little time to diagnose the failure or complete a normal return.

The engine monitor preserved a clue

The airplane carried an engine monitor recording exhaust-gas temperature, cylinder-head temperature and turbine-inlet temperature. The recorded data showed a rapid fall in turbine-inlet temperature about 45 seconds before changes in the other temperature parameters associated with the two power-loss events. Similar turbine-inlet-temperature drops appeared in three other recorded sessions without corresponding engine-power losses. The data therefore demonstrated an unusual indication but did not establish it as the cause of the failures.

The wastegate finding was not the answer

Examination found a hole in the turbocharger's automatic wastegate-controller diaphragm. That damage would allow the wastegate to fail toward the closed position. Investigators determined that a closed wastegate could increase manifold pressure and reduce turbocharger efficiency at higher altitudes, but it would not itself explain a complete loss of engine power. The final investigation therefore did not convert the physical defect into a cause that the evidence could not support.

The decision to fly again mattered

What the Records Show separated the unresolved mechanical question from the operational decision. Investigators could not determine why the total power loss occurred, but they could determine that the airplane was flown again without the partial loss of power from the previous flight being fully troubleshot. That distinction is important because the investigation did not claim that the wastegate diaphragm caused the crash.

The investigation could not determine why power was lost

The NTSB probable-cause finding states: ‘The total loss of engine power for reasons that could not be determined based on available evidence and the pilot's decision to take off without fully troubleshooting the partial loss of engine power that occurred during the previous flight.’

Accident Facts

Sources

• Aviation Safety Network record cited: https://aviation-safety.net/wikibase/228924
• Aviation Safety Network record: https://aviation-safety.net/wikibase/228924