What happened
On 11 February 2021, an Airbus AS 365 N3, registration F-GYLH, was conducting a night VFR mission near Le Havre, France. The flight's objective was to hoist marine pilots onto two oil tankers. After departing Le Havre-Octeville airport, the pilot attempted to engage the autopilot's heading and altitude hold modes. However, while the heading mode was successfully engaged, the altitude hold mode was not actually activated.
As the helicopter began a left turn, it entered a gradual descent at a vertical speed of approximately -740 ft/min. During this period, the crew was heavily engaged in radio communications with the vessels and using the onboard weather radar and AIS to locate the targets. The pilot did not notice the descent or the radio altimeter warnings, which triggered at 500 ft and 300 ft. The aircraft reached a minimum altitude of 59 ft and its speed increased to 158 kt, exceeding the maximum never-exceed speed (VNE) by 8 kt. The descent was only interrupted when a passenger alerted the crew that the aircraft was flying very low.
The investigation
The BEA examined the flight data recorder, cockpit voice recordings, and the aircraft's technical systems. The investigation revealed that the pilot believed the altitude hold mode had been engaged as part of a routine single-motion action. The investigation also scrutinized the operator's management system, noting a period of social and operational instability within the company. Furthermore, the BEA identified a technical fault in the Multi Flight Data Acquisition Unit (MFDAU) that caused intermittent breaks in the flight data recording, though the cockpit voice recording remained complete.
Findings
Several factors contributed to the near-collision:
- Failure to monitor flight parameters, specifically altitude, speed, and autopilot modes, due to high workload during the mission.
- Low salience of warnings, as the pilot and hoist operator did not notice the aural and visual radio altimeter alerts while focused on communications and vessel identification.
- Inadequate flight procedures, including an Operations Manual that did not mandate the engagement of altitude hold mode during the cruise phase at night, and a lack of required checklists for this short flight phase.
- Inconsistent application of procedures, where required autopilot mode call-outs were not systematically performed.
- Training gaps, specifically the use of newly recruited hoist operators with no prior flight or hoisting experience, which reduced the margin for error in a single-pilot operation.
Safety action
Following the incident, the operator implemented several safety improvements, including:
- Redesigning flight procedures and checklists to include a specific cruise checklist requiring the engagement of altitude and heading modes during night or IFR flights.
- Implementing a mandatory call-out and verification system between the pilot and the hoist operator regarding autopilot modes.
- Outsourcing initial technical and hoisting training for new operators to specialized organizations.
- Seeking technical solutions to increase the audibility or visibility of radio altimeter warnings.