What happened
On 2 April 2022, a Piper PA-23-250, registration G-BJNZ, was conducting a private IFR flight from Le Touquet to Wellesbourne. While cruising at FL90, the pilot noticed oil leaking from the left engine, which was soon followed by noticeable engine vibration. In response, the pilot shut down the left engine and feathered the propeller.
Despite being offered a diversion to Southend Airport by ATC, the pilot elected to continue toward the original destination, descending through controlled airspace and eventually cancelling the IFR flight plan. As the aircraft reached 2,000 ft, the pilot found it impossible to maintain level flight on the remaining right engine. The aircraft began to lose airspeed and altitude, prompting the pilot to identify a nearby grass field for an emergency landing. The aircraft landed heavily in a field near Enfield, causing the landing gear to collapse and resulting in damage to the engines, propellers, and fuselage. There were no injuries to the pilot or the three passengers on board.
The investigation
The AAIB investigation focused on the mechanical failure of the left engine and the performance of the right engine. Examination of the left engine revealed that the No 5 cylinder had failed due to a fatigue crack in the steel barrel, which had originated from a corrosion pit on the outer surface.
Regarding the right engine, testing on a dynamometer revealed a significant power deficit; the engine produced only 203 hp, approximately 19% less than its rated 250 hp. This loss of power was attributed to severe wear on the second camshaft lobe, which reduced the lift of the inlet valves for two cylinders. The investigation also noted that the annual maintenance inspection had failed to record the maximum static engine RPM, which would have provided a means to detect this power degradation.
Findings
- The left engine failure was caused by a fatigue crack in a cylinder barrel originating from a corrosion pit.
- The aircraft was unable to maintain level flight due to a combination of reduced power from the right engine and prevailing weather conditions, including potential downdrafts from nearby cumuliform clouds.
- The pilot's decision to continue the flight despite the engine shutdown was likely influenced by high workload and plan continuation bias.
- The maintenance records showed that while cylinder corrosion was visible, it was not deemed a reason for rejection by the engineer.