What happened
On September 25, 2017, at approximately 16:30 LMT, a Guimbal Cabri G2 was conducting training flights at the airfield in Sochaczew. The crew, consisting of an instructor and a student, was performing a simulated autorotation with a throttled engine. The flight plan intended for the crew to execute a flare and transition into a second circuit once power was restored.
During the flare maneuver, the engine experienced a sudden and significant drop in RPM, falling below 2000 RPM. The instructor responded by increasing power via the twist grip, which prevented an uncontrolled impact with the ground. During the subsequent descent, the governor warning light began flashing. Upon landing and shutting down the engine, a "throttle failure" message appeared on the onboard systems display.
The investigation
The investigation focused on the reported engine malfunction and the subsequent error message. Following the incident, the aircraft operator notified the CAMO Manager and the Maintenance Organization Manager. A mechanic from the maintenance organization inspected the throttle position measurement system in accordance with the manufacturer's maintenance manual (MM72-A10).
During the ground inspection, the mechanic found no evidence of the malfunction reported during the flight, nor did the onboard systems display any errors during post-flight checks. A subsequent test flight was conducted, which confirmed that the aircraft was operating normally both in flight and during post-flight system checks.
Findings
- The primary factor was a sudden drop in engine RPM during the flare phase of a simulated autorotation.
- The aircraft was returned to service after inspections and test flights failed to replicate the reported engine power loss or the throttle failure message.