What happened
On 12 March 2000, a Piper Cherokee PA-28-140, registration EI-CGP, departed Cork Airport for a training flight near the Bandon area. During the initial climb, the instructor noticed the engine was failing to produce full power despite the throttle being at maximum settings. Upon checking the gauges, the pilot discovered that the engine oil pressure had dropped to zero.
As the engine began to run roughly, the pilot declared an emergency with Cork Approach. Shortly after, the propeller ceased rotating. The pilot identified a suitable landing site in a harrowed field near Knocknacertra, avoiding a nearby field containing cattle. The aircraft performed a successful forced landing on the dry, ploughed surface, which resulted in a short landing run. Both the pilot and the student exited the aircraft without injury, though the engine sustained significant internal damage.
The investigation
The AAIU examined the wreckage and found fragments of the engine crankcase, the crankshaft forward bearing, and the No.1 connecting rod big end bearing scattered on the engine cowling. The investigation revealed that one of the engine oil bungs was missing, while the other remained in place but was not wire-locked.
It was established that during a recent oil change, the oil bung had been removed and replaced but not secured with wire locking. The maintenance organization, which utilized an apprentice mechanic, had recently performed an annual check on the aircraft. The investigation found that the inspector had overlooked the lack of wire locking, partly because other aircraft in the same fleet used quick-release bungs that did not require such security.
Findings
- The engine failed due to oil starvation caused by the loss of the oil sump bung during flight.
- The unsecured bung became loose due to engine vibrations and eventually fell out, allowing the engine oil to drain.
- The loss of lubrication led to the rapid mechanical failure of the crankshaft bearing and the No.1 connecting rod big end bearing.
- The maintenance inspection process failed to verify that the wire locking of critical engine components had been completed.
Safety action
- The maintenance contractor was advised to implement a duplicate inspection procedure for essential tasks, such as the wire locking of engine components.
- It was recommended that the contractor establish a formal training program for the apprentice mechanic to ensure proper classroom instruction and qualification.