What happened
On 24 October 2008, a Boeing 737-600, registration LN-RPW, was operating a scheduled commercial flight from Oslo/Gardermoen to Stockholm/Arlanda. Approximately 15 minutes into the flight, while cruising at FL 300, the crew and cabin staff detected a smell of burning electronics. Shortly after, the master warning and left generator warning lamps illuminated.
In response to the developing situation, the pilots descended to FL 110 and declared an emergency. To ensure passenger safety, the crew decided to divert to Västerås airport, which they identified as the most suitable alternative. During the descent, the smell intensified, prompting the crew to don oxygen masks. Upon landing at Väster äras, the aircraft was stopped on the runway, and an emergency evacuation was ordered. While the evacuation via the left-side doors was successful and resulted in no injuries, the right-side service doors proved difficult to open, and the automatic escape slides failed to inflate.
The investigation
The Swedish Accident Investigation Board (SHK) examined the electrical systems and the failure of the evacuation equipment. The investigation focused on the cause of the overheating in the electronics bay and the mechanical issues preventing the proper deployment of the emergency slides.
Findings
- The primary cause of the burning smell and warning lights was an electrical flash-over occurring in a connector within the left engine generator system, located on the engine firewall.
- This flash-over caused an overload that led to the overheating of the Generator Control Unit (GCU) located near the cockpit.
- A similar fault had been previously addressed by the manufacturer via Service Bulletin 737-24-1176, which recommended repositioning certain connector pins to mitigate flash-over risks. Although this modification was applied to the aircraft, the fault persisted.
- The difficulty in opening the right-side service doors and the failure of the automatic slides were due to the release wires being incorrectly positioned, causing them to catch in the locking mechanism of their storage boxes.
- This specific malfunction of the escape slide release mechanism had been observed on other aircraft of this type previously.
Safety action
Following the incident, the operator implemented a special check to ensure the correct placement of the escape slide release wires. The aircraft manufacturer and the slide manufacturer are also collaborating to develop a permanent solution for the door and slide deployment issue.