What happened
On 2 March 2021, a Piper PA30, registration N7977Y, was conducting a training flight from Toussus-le-Noble toward Pontoise. The crew, consisting of a pilot and an instructor, was performing an airport circuit at Pontoise. During the left-hand downwind leg for runway 05, the right engine experienced a significant power decrease.
Upon taking control, the instructor applied full power to both engines but found that the remaining left engine could not provide sufficient thrust to maintain level flight. The instructor subsequently shut down the failed right engine, feathered the propeller, and retracted the landing gear and flaps. Realizing the aircraft could not reach the runway, the instructor informed air traffic control of the intention to land in a field. The left engine was shut down shortly before impact. The aircraft landed in a ploughed field, sliding approximately 6/0 meters. Both occupants were uninjured.
The investigation
The BEA examined the wreckage and performed engine tests on a test bench. The investigation focused on the right engine's failure and the left engine's performance. Investigators found that the right engine's injector nozzle for cylinder No. 3 was clogged with material. Furthermore, the Fuel Servo Injector (FSI) strainer for the right engine was found to be distorted, which allowed fuel to bypass the filter.
Testing of the left engine revealed that while it could deliver expected maximum power, it exhibited erratic responses and "stepped" speed increases during rapid power applications. The investigation also noted several maintenance anomalies, including loose engine nuts and a detached vent hose. The aircraft's maintenance history showed that the engines had not undergone a major overhaul in decades, and the last annual inspection in January 2021 had not detected the distorted FSI strainer.
Findings
- The right engine failure was caused by the clogging of the injector nozzle due to contamination that bypassed the faulty strainer.
- The distorted FSI strainer was not detected during the previous annual inspection because the distortion did not prevent easy installation.
- The inability to maintain level flight was likely contributed to by a possible late retraction of the landing gear and a lack of sufficient power from the left engine.
- The left engine's performance was likely compromised by incorrect FSI adjustments, resulting in an overly rich air-fuel mixture.
- Maintenance anomalies suggested a lack of rigor in recent maintenance operations.