What happened
On November 17, 2018, a pilot was conducting a wave soaring flight near Hildesheim under easterly wind conditions. During the climb, the pilot noticed fluctuations in propeller RPM, which he attributed to potential carburetor icing. To mitigate this, the pilot adjusted the choke settings and, upon reaching approximately 1,200 m AMSL, shut down the engine to transition into a gliding configuration. During this process, the pilot closed the engine compartment cooling flaps to retain heat.
Shortly after the engine shutdown, the pilot felt a dull impact, described as a "kick," against his back. Despite this, no smoke or heat was immediately detectable in the cockpit, and the pilot proceeded with a standard approach and landed successfully on runway 07. However, after exiting the aircraft on taxiway B, the pilot observed small flames and smoke emanating from the left side of the engine compartment. The fire spread rapidly, causing the rear fuselage to sag and the cockpit area to be engulfed in flames, ultimately destroying the aircraft.
The investigation
The BFU examined the wreckage and the pilot's testimony to determine the origin of the fire. The investigation focused on the engine compartment, specifically the dual carburetors and the fuel delivery system. Investigators noted that the engine's structural components, including aluminum and steel parts, showed signs of extreme heat, with temperatures estimated between 700 and 1,000 °C. The investigation also looked into the aircraft's history, noting a previous water landing in 2007, and assessed the condition of the fire-retardant coating on the composite fuselage.
Findings
- The fire likely originated in the engine compartment during flight due to a deflagration (puff/explosion).
- A fuel-air mixture, possibly caused by fuel leakage from the carburetors or fuel overflow during choke adjustments, accumulated in the engine compartment.
- The accumulation of this mixture reached an ignitable concentration and was ignited by hot engine components.
- The fire-retardant coating on the composite material was likely degraded due to a previous water landing and had not been renewed.
- The intense heat caused the structural integrity of the engine mount to fail, leading to the cockpit tilting upward and exposing it to the flames.
- An easterly wind contributed to the spread of the fire, specifically affecting the right wing more significantly than the left.