What happened
On September 1, 2016, a Robin DR 400/140 B departed from Leutkirch-Unterzeil airfield for a local sightseeing flight with two passengers. Shortly after takeoff, the pilot reported engine problems to the airfield controller, noting that various warning lights were illuminated. Radar tracking showed the aircraft flying south along the A 96 motorway at approximately 3,300 ft AMSL.
Following the engine failure, the aircraft entered a glide. While the pilot attempted to manage the situation, the aircraft's speed decreased significantly. The aircraft eventually entered an uncontrolled flight state, impacting the ground in a right-hand turn with a 45-degree longitudinal pitch. The impact resulted in 3 fatalities and the total destruction of the aircraft.
The investigation
The BFU examined the engine's FADEC data, which revealed that the pilot attempted to manipulate the power lever for approximately 45 seconds in an effort to restart the engine. The investigation also focused on the engine's mechanical condition and the maintenance records of the aircraft.
Technical analysis of the engine revealed a broken timing chain. Microscopic examination showed that the chain had experienced significant wear and fatigue, with elongation reaching 1.2%, far exceeding the manufacturer's limit of 0.5%. The investigation also scrutinized the maintenance chain of responsibility, involving the aircraft owner (a flying club), the maintenance organization, and the regulatory authority (LBA).
Findings
- The primary cause of the engine failure was the rupture of the timing chain due to excessive wear and dynamic stress.
- The engine had exceeded its recommended operational interval for a timing chain replacement; the chain was used for 1,464 hours, whereas the manufacturer's guidelines and relevant Airworthiness Directives necessitated replacement much earlier.
- A series of administrative and oversight errors prevented the timely replacement of the chain. An incorrect entry in the engine logbook suggested the service was not applicable, and a flawed maintenance program (IHP) incorrectly stated that the required replacement was addressed during the last overhaul.
- The pilot's attempt to restart the engine consumed critical time during the emergency.
- The pilot failed to maintain the required glide speed, leading the aircraft into an aerodynamic stall and an uncontrolled descent.
- High stress levels during the emergency contributed to the loss of control.