What happened
On February 14, 2024, an Elixir Aircraft Elixir, registered F-HKEC, was conducting a maintenance check flight at La Rochelle - Île de Ré airport. The flight was intended to calibrate an Angle of Attack (AOA) sensor. During the initial climb, the pilot noticed that the elevator control had become free in movement. The pilot managed to maintain the pitch attitude using engine power and the electric elevator trim.
Following the discovery, the additional pilot declared an emergency to request a return to the aerodrome. During the approach, the aircraft was flying at approximately 85 knots. The pilot attempted to land without using flaps to avoid changing the aircraft's configuration. Upon touchdown, the aircraft bounced. The pilot initially attempted a go-around but, after deciding to try the landing again, lost control of the pitch attitude. The aircraft subsequently made a hard contact with the runway, causing the nose gear to break and the aircraft to come to rest at the edge of the runway.
The investigation
The investigation focused on the mechanical failure of the elevator control system. Investigators recovered a screw and washer from the keel area under the fin. These components were identified as part of the assembly connecting the elevator control's vertical rod to the bellcrank. The associated Nylstop nut was missing. The investigation established that the vertical rod had disconnected from the bellcrank because the screw was not properly secured.
Regarding maintenance, the investigation examined the recent work performed by the Elixir Aircraft Combined Airworthiness Organisation (CAO). The mechanic had recently performed adjustments to the elevator fairing. The investigation also looked into the organizational structure of the CAO, noting that the technical manager was also the sole person responsible for maintenance and airworthiness management, and that the maintenance workspace was subject to frequent interruptions.
Findings
- The primary cause of the flight control failure was the omission of a nut during the reassembly of the elevator control assembly.
- The mechanic was likely interrupted during the reassembly process due to being called away for production line inspections.
- The maintenance professional was under significant time pressure due to a high workload and mandatory inspections of the fleet.
- The task was not classified as a critical task by the technical manager, which meant no independent inspection or cross-check was performed after the assembly was completed.
Safety action
Following the accident, Elixir Aircraft implemented several measures, including:
- Segregating production and maintenance workshops to prevent interruptions.
- Recruiting additional mechanics dedicated specifically to CAO activities.
- Implementing an extended pre-flight inspection involving a mechanic following any critical maintenance task.
- Adopting a policy of systematic replacement of Nylstop nuts during disassembly.