What happened
On 9 July 2021, a Diamond Aircraft Industries HK36TTC motor glider, registered HB-2314, departed from Locarno Airport (LSZL) for a flight to Italy. Shortly after takeoff during the initial climb, the pilot and passenger noticed a strange odor in the cockpit. Within thirty seconds, a thick curtain of smoke began to fill the cabin, appearing to originate from the baggage area behind the occupants.
Despite the cockpit windows being open, the smoke density increased rapidly. The pilot immediately requested an emergency return to the airport. Air traffic controllers observed a heavy trail of white smoke trailing from the aircraft' and alerted the military air base fire brigade. The pilot executed a straight-in approach and landed on the grass runway 08R approximately six minutes after departure. The engine was shut down immediately upon landing, and the crew evacuated without injury, though the aircraft sustained slight damage.
The investigation
Investigators examined the engine's Turbocompressor Control Unit (TCU) data, flight path recordings, and communications with air traffic control. Post-landing inspections of the engine compartment revealed that the oil tank was nearly empty, with black oil dripping from the exhaust pipe.
Technical analysis focused on the turbocharger, where investigators found significant foreign object damage (FOD) on the impeller and housing. Furthermore, a broken exhaust gas temperature sensor was discovered upstream of the turbocharger within the exhaust manifold. The investigation also looked into the engine's lubrication history and the chemical composition of the oil used in the engine.