Incident Overview
On 31 January 2015, a Boeing 737-800 operating a flight experienced a flap malfunction while configuring for landing at EFKT. The flaps jammed at position 1, prompting the crew to request holding clearance from air traffic control. The flight crew then executed the 'TRAILING EDGE FLAP DISAGREE' checklist.
Crew Actions
Following the checklist, the crew proceeded with an alternate flap extension method and configured the aircraft to land with flaps at position 15. After landing, the crew observed significant icing on the aircraft. The aircraft was subsequently de-iced, after which a full flap extension and retraction test was performed successfully.
Post-Flight Maintenance
On the return flight, after the aircraft reached its base, maintenance personnel conducted a test of the Flaps/Slats Electronic Unit (FSEU), which showed no system errors. Connectors in the flap extension and retraction system were cleaned. Additionally, the FSEU was replaced in accordance with AMM 27-51-01/401. A subsequent system test passed, and the aircraft was returned to service without restrictions. The fault did not recur on subsequent flights.
Occupants and Injuries
The aircraft carried 189 occupants. No injuries were reported.
Probable Cause
Investigation determined that the most probable cause of the flap malfunction was blockage of the flap extension system during approach due to severe aircraft icing.