What happened
On July 2, 2012, an Aquila A210 was conducting a cross-country flight from Brussels (EBCI) toward the Netherlands (EHLE). While cruising near Brussels Airport, the two crew members noticed the smell of burning oil, though no smoke was visible and engine parameters remained normal. Shortly after passing the NIK VOR, the engine began running roughly and experienced a significant drop in oil pressure.
To stabilize the engine RPM, the pilot adjusted the propeller to a fine pitch. After identifying a suitable landing site in a grass field in Waasmunster, the pilot performed two circling maneuvers before executing a successful forced landing. There were no injuries to the two occupants. Upon inspection, the aircraft's belly showed a heavy oil trail, and the nose landing gear cowling had been ruptured.
The investigation
The AAIU(Be) examined the engine and the aircraft's maintenance history. The engine, powered by a Rotax 912S, was sent to Germany for detailed analysis. Investigators discovered a hole in the ignition housing located beneath the water pump. Upon further disassembly, a damaged thrust washer from the idle/intermediate gear was found, along with a missing tooth from the camshaft gear and damage to the water pump gear.
Maintenance records showed that the sprag clutch assembly had been replaced just 14 flight hours prior to the incident by an independent technician. While the technician did not remove the intermediate gear during the repair, the Rotax Maintenance Manual specifies that the gear should be removed to facilitate cleaning and visual inspection. The investigation focused on how the washer became displaced.
Findings
Investigators determined that the loose washer was the primary cause of the incident. It is believed that during the recent maintenance of the sprag clutch, the gear shaft moved along with the ignition housing, causing the aft thrust washer to shift out of position. This displaced washer eventually became lodged between gears, leading to the breakage of a camshaft gear tooth. The resulting debris was forced through the ignition housing, creating the hole that caused the oil leak and subsequent engine failure.
Safety action
Following the investigation, the AAIU(Be) issued recommendation 2012-P-14, suggesting that BRP-Powertrain include a specific warning in the Maintenance Manual. This note would alert users that failing to verify the presence of both thrust washers on the intermediate gear before reinstalling the ignition housing could result in catastrophic engine damage.