What happened
On October 18, 2008, a Pottier P 220 aircraft, registration F-PABJ, departed from Sisteron aerodrome for a local test flight following maintenance. During the initial climb, the aircraft's engine experienced intermittent misfires and power loss. Witnesses observed the aircraft failing to gain sufficient altitude, subsequently entering a left-hand turn and descending toward the Durance river valley. The aircraft eventually struck a tree and came to rest in a field near a cliffside. The impact was moderate, but the pilot was found outside the cockpit.
The investigation
The investigation focused on the mechanical state of the engine and the structural integrity of the cockpit safety equipment. The aircraft was powered by a modified Volkswagen 2000 automobile engine. Investigators discovered that the pilot, who was also the aircraft's builder and owner, had recently performed engine swaps and adjustments.
Technical examination of the engine revealed several critical irregularities. The electrical fuel pump was being supplied with 12 volts instead of the required 24 volts, and the pump was incorrectly specified for kerosene rather than gasoline. Furthermore, the carburetor needle valve guide had been broken due to excessive tightening. The cylinder heads had been modified to accommodate a dual ignition system consisting of both a magneto and a manual distributor; however, the camshaft and tappets showed significant wear, and valve clearances were found to be approximately 4mm, which is ten times the nominal tolerance. Additionally, the magneto was coupled to the engine using a piece of cooling hose, which created a phase shift between the engine speed and the ignition timing during power changes.
Findings
- The primary cause of the accident was improper engine maintenance and modifications performed without following standard engineering practices.
- The engine's ignition timing was inconsistent due to the lack of synchronization between the two ignition circuits and the use of an improper flexible coupling.
- A contributing factor to the fatality was the under-dimensioned attachment of the lap belt to the airframe, which caused the belt to tear away from the structure during the impact, ejecting the pilot from the cockpit.
- The aircraft was destroyed in the accident, and the pilot, a highly experienced flyer with over 2,000 total hours, was killed.