What happened
On 28 May 2023, an Air France Airbus A350-900, registration F-HTYO, was operating flight AF291 from Osaka (Kansai International Airport) to Paris-Charles de Gaulle. During the initial climb, the crew encountered weather radar faults. After attempting to troubleshoot the systems, the crew decided to perform an in-flight turn-around and return to Osaka due to the loss of radar capability and the presence of cumulonimbus clouds along the planned route.
While descending through FL 300, the crew heard a loud thud and significant aerodynamic noise. The radome had collapsed on itself. This structural failure caused substantial airflow disturbances that affected the aircraft's pressure probes. Consequently, the crew observed fluctuating and unreliable airspeed indications on the primary flight displays, particularly as the aircraft was configured with slats and flaps for approach. Due to these discrepancies, the crew disconnected the autopilot and autothrust. The aircraft subsequently performed an overweight landing in Osaka without further incident.
The investigation
The BEA investigation focused on why the damage to the radome was not detected during previous maintenance and why the crew experienced unreliable airspeed indications. The investigation examined the maintenance history of the aircraft, specifically looking at whether the radar faults previously reported had been properly addressed. Investigators also analyzed the Airbus A350's NAIADS system and how the aerodynamic disturbances from the damaged radome interacted with the aircraft's air data probes.
Findings
- A structural failure of the radome occurred during flight, which was preceded by intermittent weather radar faults.
- The damage to the radome's internal structure was not detectable on the ground through standard radar testing, as the deformation of the composite structure changed during flight.
- The airflow disturbances caused by the damaged radome impaired the pressure measurements of the airspeed probes, leading to the unreliable airspeed indications.
- Maintenance procedures at the time did not explicitly mandate the inspection of the radome's inner surface following radar faults or suspected strikes, allowing the internal debonding to go unnoticed.
- The crew's management of the unreliable airspeed procedure was complicated by the NAIADS system, which kept automatic systems available despite the fluctuating data.