What happened
Between September 2024 and April 2025, three separate incidents involving Airbus neo-family aircraft were investigated following significant disruptions to communication, surveillance, and navigation systems.
On 20 September 2024, an Airbus A320neo, registered EI-NSF, operated by Aer Lingus, experienced a sudden failure of its communication and transponder systems while cruising at FL 330. The crew reported audio crackling and erratic behavior on the Radio Management Panels (RMPs). The aircraft disappeared from radar contact, prompting the activation of the ALERFA phase. During the incident, the aircraft came within 3.2 NM horizontally and 175 ft vertically of another flight, highlighting a dangerous loss of separation. The crew eventually landed at Bordeaux-Mérignac after re-establishing contact via the emergency frequency.
On 13 January 2025, an Airbus A321neo, registered PH-YHA, operated by Transavia, experienced similar failures. The aircraft's transponder began transmitting random codes, and the crew lost the ability to change radio frequencies. The aircraft was forced to divert to Bordeaux-Mérignac, where it was eventually grounded after a subsequent flight showed persistent transponder anomalies.
On 29 April 2025, an Air．Airbus A321neo, registered PH-YHC, also operated by Transavia, experienced a loss of radar contact and radio degradation. The crew was forced to perform 360-degree turns to avoid entering restricted airspace after the aircraft was refused entry by Brussels ACC. A near-miss occurred when the aircraft closed to within 3.9 NM of another flight, as the transponder failure prevented TCAS and ATC safety nets from detecting the conflict.
The investigation
The BEA investigation focused on the Digital Radio and Audio Integrated Management System (DRAIMS), which manages VHF/HF radios, transponders, ACAS, and radio navigation. 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 leads to erratic data processing, resulting in desynchronized RMPs, loss of audio quality, and the transmission of incorrect transponder codes or altitude information.
Findings
- The primary cause of the failures is a software-related vulnerability in the AMU that leads to erratic processing of Ethernet data flow.
- The failure is unpredictable and can cause a wide range of symptoms, including the loss of CPDLC, SATCOM, and TCAS functionality, as well as the inability to select navigation frequencies.
- The investigation noted that reliance on third-party flight tracking tools like Flightradar24 can be misleading during transponder failures, as these sites may show extrapolated paths rather than actual aircraft positions.
- Current radio failure procedures in some French control centers may be insufficient, as some units lack the ability to transmit on the 121.5 MHz emergency frequency, which is often the only remaining communication channel during a DRAIMS failure.