What happened
On January 1, 2016, a Robin DR400-155 CDI 'Ecoflyer', registration F-HCAP, departed Cannes Mandelieu airport for a flight to Villanova d’Albenga, Italy. The aircraft was carrying a pilot and three passengers, operating near its maximum takeoff weight.
During the initial climb, at approximately 500 feet, the pilot noted a slight burning odor accompanied by rapid engine power fluctuations. As the aircraft reached 800 feet, the burning smell intensified, and FADEC warning lights for both channels illuminated, signaling a significant drop in engine power. The pilot declared an emergency, performed a 180-degree turn, and returned to land on runway 35. The aircraft landed at a high speed, near its maximum flap-extended velocity, and came to a stop on a taxiway. The engine was no longer driving the propeller, preventing the aircraft from taxiing to the parking area. There were no fatalities or injuries.
The investigation
The investigation focused on the engine's performance and the FADEC data. Analysis of the FADEC records showed that while fuel pressure remained stable, the engine speed fluctuated rapidly two minutes after takeoff.
An examination of the Thielert engine by the manufacturer revealed that the torque damper had been contaminated with oil. This contamination caused a loss of friction between the damper discs, which prevented the engine from effectively driving the propeller. The leak originated from a seal between the lubricated engine drive shaft and the non-lubricated torque damper. Investigators discovered abnormal oblique scratches on the drive shaft surface, which were traced back to an improper manual polishing procedure performed during a previous maintenance session by the manufacturer.
Findings
- The primary cause of the power loss was oil contamination of the torque damper.
- The contamination was caused by an oil leak through a seal, resulting from improper manual polishing of the drive shaft during prior maintenance.
- The loss of friction between the damper discs led to the reduction in power transmitted to the propeller.
- The pilot was able to complete the emergency turn and landing due to residual friction that allowed some power to still reach the propeller.