What happened
On April 29, 2017, at 08:12 UTC, a Boeing 737-800 was performing a takeoff from runway 27 at Warsaw Chopin Airport (EPKT) for a scheduled flight to LLBG. During the takeoff roll, as the aircraft reached a speed between 80 knots and V1 (110 knots), the crew received a T/O Configuration Warning indicating the aircraft was not properly configured for departure.
In response to the warning, the crew aborted the takeoff and taxied the aircraft to the first available taxiway. During the taxi, the crew observed an asymmetry in the flap position via the TE Flaps indicator, noting the left side at -5 degrees and the right side at over 5 degrees. This discrepancy had not been present prior to the start of the takeoff roll. Even after the crew attempted to retract the flaps to the "UP" position, the asymmetry persisted, with the left side at -1 degree and the right side at -1.5 degrees. The captain subsequently decided to return the aircraft to the apron.
The investigation
Following the incident, the aircraft was handed over to maintenance personnel. Technical staff performed an operational test of the Flap Slat Electronic Unit (FSEU). This testing revealed a malfunction in a specific sensor, identified as FLAP SKEW nr 6.
Findings
- The primary cause of the incident was a malfunction of the FLAP SKEW nr 6 sensor within the flap extension system.
- Maintenance actions included the replacement of the faulty sensor and the flap position indicator.
- Subsequent testing of the flap system confirmed that the malfunction was resolved, and the aircraft was returned to service.