What happened
A charter flight operating a Boeing 737-800, registration OY-JZN, was en route from Hurghada to Billund when unexpected headwinds led to higher than anticipated fuel consumption. During the approach to Billund, the aircraft encountered significant windshear, prompting the flight crew to execute a missed approach.
During the subsequent climb-out, a technical malfunction occurred within the flap drive system. As the crew attempted to retract the flaps to 15°, a flap overspeed event occurred. This triggered the Flap Slat Electronic Unit (FSEU) to command an automatic retraction. Simultaneously, a failure in a flap solenoid valve prevented it from resetting, causing the flaps to retract to 13° before the FSEU removed power to the drive system to prevent uncommanded motion.
The resulting stuck flap configuration increased aerodynamic drag, further accelerating fuel consumption. Faced with a rapidly diminishing fuel supply, the crew diverted to Copenhagen, Kastrup (EKCH). To manage the situation, the crew declared a fuel emergency, which secured ATC priority and direct routing. The aircraft eventually landed at Copenhagen with 999 kg of fuel, which was 119 kg less than the required minimum final reserve.
The investigation
The Danish Accident Investigation Board examined the sequence of events, focusing on the mechanical failure of the flap system and the fuel management decisions. The investigation looked into the flight planning process, noting that the crew had relied on an outdated Operational Flight Plan (OFP) that did not reflect the most recent winds aloft forecasts.
Investigators also analyzed the flap drive system, identifying that a flap solenoid valve failed to reset following a load relief event. The investigation confirmed that the crew's decision to divert to Copenhagen was a rational response to the technical failure and the deteriorating weather conditions, despite the resulting fuel shortage.