What happened
On January 3, 2003, a Cessna 172 R, registration F-GLTR, departed from the Courchevel altiport for a flight to Cuers. During the initial climb, the pilot noticed a drop in engine power and elected to divert to Albertville aerodrome.
While established on the final approach for runway 23, the aircraft experienced a bounce upon touchdown. Attempting to execute a go-around, the pilot applied full throttle and retracted the flaps. However, the engine failed to provide sufficient power, with the RPM unable to exceed 1,700. Consequently, the aircraft failed to climb, struck two rows of hedges, and performed an emergency landing in a nearby field. The aircraft sustained heavy damage.
The investigation
The investigation focused on the engine's performance and recent maintenance history. The aircraft had undergone a 50-hour inspection and engine overhaul in late 2002. During the examination of the engine, investigators found that when the throttle was advanced to full power, the engine RPM systematically dropped to between 1,600 and 1,700 RPM.
Testing of the fuel injection unit revealed that fuel flow measurements were significantly outside of manufacturer limits. Upon disassembly of the injection block, investigators discovered that the Nylstop nut used to secure the fuel flow adjustment screw had not been properly tightened and, crucially, lacked the required application of Loctite adhesive to prevent loosening.
Findings
- The primary cause of the engine malfunction was the incomplete execution of a maintenance task, specifically the failure to apply Loctite to the fuel flow adjustment screw nut.
- Vibrations from previous flights likely caused the unsecured screw to gradually loosen, eventually leading to a significant reduction in fuel flow and engine power during the climb.
- The pilot's approach to the diversion aerodrome was unstable, characterized by an excessive approach speed and altitude.
- The decision to attempt a go-around with a malfunctioning engine was inappropriate, and the subsequent retraction of flaps during the maneuver further degraded lift, preventing the aircraft from climbing over the obstacles.