What happened
On 14 April 1998, a Boeing 737-5L9, registration G-MSKA, was conducting a passenger flight toward Birmingham Airport when a fire broke out in the forward galley. The incident began during the descent when a single meal was briefly placed in the number one oven. Although the oven was switched off after one minute of use, a burning smell soon became noticeable to the crew.
Upon inspection, the cabin crew observed a bright red glow emanating from behind the rear internal panel of the oven. The purser notified the flight deck, prompting a PAN call and an expedited approach by air traffic control. Despite the crew discharging two BCF fire extinguishers into the unit, the fire appeared to intensify, leading the pilots to upgrade the emergency to a MAYDAY. The flight crew informed controllers of their intention to stop on the runway to evaluate the situation before deciding whether to evacuate. Once the aircraft came to a halt, the purser determined the fire was extinguished and safe to taxi to the gate under fire brigade escort.
There were no fatalities and no injuries to the 49 passengers or 7 crew members on board, and the aircraft sustained no damage.
The investigation
Investigators examined the oven and its electrical components to determine the source of the heat. While initial inspections of the unit while installed in the aircraft showed no defects, subsequent workshop examinations revealed evidence of overheating within the heating elements. The oven operates via a 3-phase 11-volt AC system using three separate elements controlled by a common relay.
Technical analysis by an overhaul agency confirmed that one specific element had been subjected to excessive heat. The investigation focused on the electrical path, which includes a thermostatic controller, an overheat protection trip, a circuit breaker, and a galley master switch. It was noted that the crew did not attempt to trip the circuit breaker or use the galley master switch during the incident.
Findings
- The fire originated from an overheated oven element caused by a failure in the control mechanism.
- A failure in the control relay prevented one contact from opening when the oven was switched to the OFF position, meaning power remained supplied to one heating element.
- Because the fan was no longer running to distribute heat and the thermostatic control was bypassed by the relay failure, the element heated until it reached a visible red glow.
- The overheat protection trip did not activate because the temperature did not reach the necessary threshold for the trip to operate.
- The crew did not isolate the power via the circuit breaker or the galley master switch, likely because the fire was not initially identified as an electrical fault.
Safety action
- Procedures for flight deck and galley management are being reviewed following the failure to use the galley master switch or circuit breaker during the fire.