What happened
On 14 September 2020, a Grob G1lam115, registration F-GGOB, was conducting a cross-country flight from Troyes to Amboise with a pilot and one passenger on board. While cruising at 3,000 feet, the pilot detected a burning smell, which was believed to be originating from the ventilation system. To ensure safety, the pilot decided to divert to Aubigny-sur-Nère aerodrome, landing without incident.
Following the landing, the pilot performed a visual inspection and a start-up checklist. Finding no obvious anomalies and no further smell after engine shutdown, the pilot concluded the initial alert was a false alarm and proceeded to a refueling station. Upon reaching the fuel pump and shutting down the engine, the pilot and passenger observed flames and white smoke emerging from the engine compartment. The crew immediately executed emergency fire procedures and evacuated the aircraft. The fire was contained before it could spread beyond the firewall, but the aircraft sustained substantial damage.
The investigation
The BEA examined the aircraft in a hangar at Aubigny-sur-Nère. The investigation focused on the engine compartment, where soot covered the cowlings, engine, and propeller spinner. Investigators noted damage consistent with exposure to extreme temperatures on the front and upper sections of the engine up to the firewall.
Technical analysis of the oil system revealed anomalies in the breather pipe and the pressure sensor. Laboratory tests of the engine cowling and the pressure sensor confirmed that engine oil was present in the combustion residues. The investigation confirmed that the fuel system remained intact and that the fire was fueled by engine oil.