What happened
Between September 2024 and April 2025, three separate incidents involving Airbus neo-family aircraft were investigated following significant failures in communication and surveillance systems.
On 20 September 2024, an Airbus A320-251N, registered EI-NSF, operated by Aer Lingus, experienced a sudden failure of its Radio Management Panels (RMPs). The crew reported audio crackling, followed by the loss of both VHF radio communications and transponder functionality. The aircraft disappeared from civil radar, prompting military coordination and the activation of the ALERFA alert phase. During the descent, the aircraft experienced a loss of separation with a British Airways flight, coming within approximately 175 feet vertically. The crew eventually landed at Bordeaux-Mérignac after re-establishing contact via the emergency 121.5 MHz frequency.
On 13 January 2025, an Airbus A321-252NX, registered PH-YHA, operated by Transavia, experienced erratic transponder behavior, including 85 Mode C losses and hundreds of unauthorized transponder code changes. The crew was unable to change radio frequencies, eventually forcing a diversion to Bordeaux-Mérignac. A subsequent flight with the same aircraft experienced similar transponder issues, leading to the aircraft being grounded.
On 29 April 2025, an Airbus A321-252NX, registered PH-YHC, also operated by Transavia, experienced a loss of radar contact and radio synchronization. The aircraft was forced to perform 360-degree turns to avoid entering restricted Maastricht airspace. During this period, the aircraft experienced a loss of separation with another flight, as the transponder was in standby mode, preventing TCAS alerts.
The investigation
The BEA investigation focused on the Digital Radio and Audio Integrated Management System (DRAIMS), which manages communications, aural alerts, and surveillance. The investigation established that a lack of robustness in an Audio Management Unit (AMU) component to Ethernet micro-cuts causes the system to enter a degraded mode. This results in erratic data processing between the RMPs and the AMU, leading to desynchronized radio frequencies, loss of audio quality, and the spontaneous switching of transponders and TCAS to standby mode.
Findings
- The primary cause of the failures is a software vulnerability in the AMU that leads to erratic processing of Ethernet data.
- The failure is unpredictable and can affect various functions, including VHF/SATCOM communications, aural alerts, and the stability of the transponder and TCAS.
- In the event of a transponder failure, reliance on flight tracking websites like Flightradar24 can be misleading, as these sites may show extrapolated paths rather than the aircraft's actual position.
- Existing radio failure procedures may be insufficient when facing simultaneous loss of both radio and transponder functionality.