What happened
On 7 June 2009, a Boeing 737-800, registration D-AHLR, operating a charter flight from Mahon, Spain, to Frankfurt, Germany, declared a Mayday distress call. While cruising at flight level 380, approximately 65 NM southeast of Geneva, the crew reported smoke of electrical origin on board. The aircraft was carrying 197 passengers, including 9 infants, and 6 crew members.
The flight crew requested an immediate diversion to Geneva airport. During the descent, the crew managed the situation effectively, eventually reporting that the smoke was under control. The aircraft landed safely at Geneva without any injuries to passengers or crew. Following the landing, the passengers were able to disembark normally.
The investigation
The Swiss Accident Investigation Board (SAIB) examined the technical components of the aircraft's passenger entertainment system, specifically focusing on the Seat Electronic Box (SEB) located under a passenger seat. The investigation analyzed flight data, cockpit voice recordings, and air traffic control communications to reconstruct the sequence of events and evaluate the crew's response to the emergency.
Findings
Technical analysis revealed that the smoke was produced by a defective SEB located under seat E in the fifth row. The investigation established that a manufacturing defect involving the assembly of a printed circuit within the audio box caused an internal short-circuit.
Regarding operational factors, the investigation noted that the crew experienced a high workload due to frequent radio communications. During the emergency, at least nine different frequency selections were made, one of which was an error that caused a temporary loss of contact with air traffic control. However, the crew's decision to divert to Geneva was deemed appropriate, and the management of the flight was conducted in accordance with manufacturer procedures.
Safety action
The investigation identified a safety deficit regarding the management of communications during distress situations. To prevent confusion and reduce crew workload, the report issued a safety recommendation suggesting that the Federal Office of Civil Aviation (FOCA) should require that a single, dedicated frequency be assigned to an aircraft in distress until it has landed.