What happened
On September 15, 2013, a Piper PA-32R, registration F-GGBD, was performing local flight maneuvers at Lille-Lesquin airport. After completing a 30-minute local flight, the pilot decided to perform two circuit patterns on runway 20. During the second circuit, while flying into a tailwind, the pilot experienced heavy engine vibrations. This was immediately followed by smoke and the projection of oil onto the engine cowling. The pilot declared an emergency and successfully performed an emergency landing on runway 08. There were no injuries reported, though the engine sustained damage.
The investigation
The investigation focused on the mechanical failure of the engine. The pilot, who had owned the aircraft since 1987 and possessed extensive experience on this type, confirmed that the oil level had been checked and was normal prior to engine start. During the flight, the pilot noted that engine temperature and oil pressure remained stable until the vibrations occurred.
Post-flight inspection revealed a perforation in the upper engine crankcase near cylinder number 6. On the ground, an oil puddle was discovered at the location where the aircraft had been parked for five minutes before takeoff. While the oil dipstick and filler cap were in place, they were found to be unlocked. The investigation could not definitively confirm whether the cap had been properly secured before the engine was started. The aircraft's last 50-hour maintenance inspection had been completed by an approved organization in May 2013, with only four flight hours accumulated since that service.
Findings
Technical analysis determined that the engine damage was caused by the failure of connecting rod number 6, which had fractured in several locations. According to the manufacturer, such a mechanical failure is typically the result of a lubrication deficiency. The investigation concluded that the failure of the connecting rod was likely caused by a lack of lubrication, which may have been triggered by an oil leak resulting from the improperly secured oil filler cap.