What happened
On November 7, 2021, during a methodical training flight at EPKA aerodrome, an EC1s35-P2 PLUS (registration SP-HXU) experienced a torque (TQ) exceedance on engine number 2. The torque reached 96.00% within 0.5 seconds.
This event followed two similar incidents occurring the previous day, November 6, 2021. During two flights simulating FADEC failures on that date, engine number 1 reached 93.6% TQ within 0.25 seconds, and engine number 2 reached 94.4% TQ within 0.875 seconds. The training flight on November 7 was specifically organized by the Head of Pilot Training to address the irregularities observed during the previous day's operations.
The investigation
The investigation examined flight data and the pilot's handling of the aircraft. Analysis of the UMS/PGS system records confirmed that the torque limits for engines number 1 and 2 (category "F") had been exceeded.
Following the exceedances, a maintenance engineer performed several inspections in accordance with the Aircraft Maintenance Manual (AMM), including checks of the main gearbox chip detector, the tail gearbox chip detector, the main rotor shaft, and the main rotor blades. No defects were found, and the aircraft was cleared for continued service.
Findings
The investigation established that the primary cause of the exceedances was improper manipulation of the twist grip during the final phase of landing while simulating FADEC failure conditions. Specifically, while the twist grip was in the "N" position, the pilot performed rapid decreases and subsequent increases in power, leading to the torque spikes.