Incident Summary
On 28 March 2023 at 1330 UTC, a Piper PA-31-350, registration G-FCSL, experienced a right engine failure while in cruise at 2,000 ft agl south of Salisbury, Wiltshire. The aircraft was on a private flight from Cardiff to its base at Shoreham with two crew and one passenger on board. No injuries were reported. The right engine's No 2 cylinder had detached from the crankcase, causing mechanical damage and superficial fire damage to the engine and cowling. The pilot conducted a successful landing at Bournemouth Airport.
Flight History
The flight was routine until, a couple of minutes after the pilot completed normal checks with both engines at 2,200 rpm, a loud bang occurred accompanied by adverse yaw. The right engine had failed. The pilot and co-pilot observed oil covering the right engine cowling, the dipstick access flap open, and a dent protruding from the cowling. After shutting down the engine and feathering the propeller, flames were seen from the right engine. The firewall fuel shutoff was activated, extinguishing the fire within about 10 seconds. A PAN call was made to Boscombe Down, and the pilot declared intentions to land at Bournemouth Airport. The left engine operated correctly throughout. The aircraft made a visual approach and landed on Runway 26 without further incident.
Engine Examination
The engine, installed in 2016, had accrued 1,000 hours of its 1,800-hour time between overhaul. No abnormalities had been noted prior. Post-incident examination revealed that the front left cylinder (No 2) had detached from the crankcase. All six attachment studs and both through-bolts were broken. A section of crankcase with two stud remains had detached and was found in the lower cowling. The piston had jammed due to ring damage, and the connecting rod had separated from the big end bearing. The cylinder inlet and exhaust manifolds were displaced. Fire damage was evident on and around the turbocharger.
Analysis and Conclusion
The cylinder mounting flange is secured by six threaded studs and two through-bolts. All studs and through-bolts showed characteristics of high-cycle fatigue failure. Three studs at the front of the cylinder (positions No 3, No 4, and No 5) exhibited different fatigue features suggestive of loss of preload. The No 4 stud's fracture face was mechanically damaged during the failure sequence, and its nut was missing. The remaining studs and through-bolts showed unidirectional bending fatigue. The loss of preload in the front studs likely created conditions for the remaining fasteners to fail. The reason for the loss of preload could not be determined. The incident was attributed to fatigue failure of the attachment studs and through-bolts, resulting in the detachment of the No 2 cylinder.