Summary
On 7 July 2012, a Piper PA 31-350 twin-engine aircraft, registration OK-EKV, experienced a left engine failure during climb after takeoff from Krakow Balice Airport (EPKK) in Poland. The crew, consisting of a pilot aged 34 with valid commercial pilot license and total experience of 1628:59 hours (99:55 on type), was conducting aerial photography. The aircraft was operated by Argus geo systém s.r.o., Czech Republic.
Incident Details
At 10:10 UTC, shortly after takeoff for the first flight of the day, the pilot heard a dull thud from the left engine, followed by vibrations, power loss, and zero oil pressure. The propeller automatically feathered. The pilot executed emergency procedures for single-engine flight and returned to EPKK with assistance from local air traffic control. The landing was safe with no damage to the aircraft or injury to the crew.
Aircraft and Engine Information
The aircraft was a 1977 Piper PA 31-350, total time 9159:55 hours. It was powered by two Lycoming TIO 540J2BD engines. The left engine, serial L-3230-61A, had accumulated 3275:50 hours total, with 1520:45 hours since its last major overhaul in 2000. It was lubricated with AeroShell 15W50 oil. Pre-flight inspection and engine run-up were normal, with oil quantity at 12 quarts in the left engine.
Technical Findings
After landing, a post-flight inspection revealed a breach in the upper crankcase of the left engine. During teardown at an approved maintenance organization, investigators found that a circular washer (p/n 71907) securing a counterweight retaining pin had fractured. The pin shifted axially, allowing a counterweight segment to dislodge. The loose counterweight struck the crankcase, breaking it, and collided with the connecting rod of cylinder six and the camshaft, causing further damage. The broken washer pieces were found in the oil pan. The opposite side of the pin remained properly secured.
Analysis
The failure occurred due to the release of a crankshaft counterweight during operation. The circular washer likely failed from material fatigue, leading to the pin displacement and subsequent engine destruction. Routine maintenance did not include specific checks of this assembly, and the defect could not be detected without engine disassembly.
Probable Cause
The cause of the incident was engine failure as a consequence of a loose counterweight for balancing the crankshaft during operation.
Safety Recommendations
The findings were provided to the engine manufacturer and EASA. The engine was sent to the manufacturer for further evaluation of the damage.