What happened
On the night of 16 November 2004, a Diamond DA 40 D aircraft, registration SE-LTP, was conducting a night navigation flight from Växjö/Kronoberg airport toward Värnamo. The flight was an instructional mission carrying an instructor, a student, and one passenger.
As the aircraft approached Värnamo, the engine revolutions suddenly surged while the oil pressure dropped to zero before fluctuating and then disappearing entirely. Shortly after, the engine ceased operation. During the failure, smoke entered the cabin, and the crew observed sparks and flames beneath the engine cowling. The instructor assumed control and performed a forced landing on an industrial estate. The landing resulted in no injuries to the occupants and only negligible damage to the aircraft.
The investigation
The Swedish Accident Investigation Board (SHK) examined the engine and analyzed operational data provided by the manufacturer. The investigation revealed that the engine's rear connecting rod bearing had seized, causing the connecting rod to break and puncture the crankcase.
Upon inspection of the engine's components, investigators found that the input shaft of the double oil pump was extremely worn. This pump is responsible for both supplying oil to the propeller for pitch adjustment and returning oil from the turbocharger. The investigation also reviewed maintenance records and a manufacturer service bulletin regarding gearbox inspections.
Findings
- The engine failure was caused by the extreme wear of the double oil pump input shaft, which prevented the pump from being driven.
- This failure caused the propeller to move to a fine pitch, leading to the sudden increase in engine revolutions.
- Simultaneously, the lack of oil return from the turbocharger caused the turbocharger's oil sump to overflow, leaking oil onto the underside of the fuselage.
- The depletion of oil eventually led to the seizure of an engine bearing and the subsequent mechanical destruction of the connecting rod.
- The engine had exceeded the 300-hour inspection interval specified in the manufacturer's service bulletin, having operated for approximately 449 hours since the gearbox installation.
- The SHK noted that the manufacturer's service bulletin was poorly phrased, as it was categorized as "information only" and did not clearly communicate that the gearbox required removal for inspection.
Safety action
Following the accident, the German civil aviation authority issued an airworthiness directive (D-2005-152). This directive made the replacement of the gearbox and oil pump mandatory under a new service bulletin. Additionally, the engine manufacturer redesigned the oil pump drive to prevent similar wear-related failures.