What happened
On June 5, 2018, a Boeing 737-800 operating at Warsaw Chopin Airport (EPWA) experienced a series of technical malfunctions involving the aircraft's leading edge flaps. Prior to the initial flight, the crew identified an incorrect position for slot number 3 and a "Leading Edge flaps transit" warning. Although maintenance replaced a sensor, which delayed the flight by approximately two hours, the issue persisted during subsequent operations.
During the first approach, the crew initially configured the aircraft for landing with flaps at 40 degrees. Upon transitioning to 25 degrees, the "Leading and Edge flaps transit" warning reappeared, accompanied by abnormal airspeed indications and low-speed buffet. The crew attempted to stabilize the aircraft by moving the flaps to 30 degrees, but the problem remained, and the aircraft briefly exceeded the flap 30 speed limit by approximately 2 knots. The crew subsequently moved the flaps to 25 degrees and, to avoid a stall warning, aborted the approach at 744 feet for a go-around. Following the non-normal checklist, the crew landed the aircraft using 15 degrees of flaps without further incident.
During the following flight leg, the crew prepared for a landing using 30 degrees of flaps, with a contingency plan to use 15 degrees if the warning recurred. However, when transitioning the flaps to 10 degrees during the approach, the "Leading Edge flaps transit" warning returned. The crew followed the non-normal checklist and landed using 15 degrees of flaps amidst turbulent conditions. The aircraft drifted approximately 1.5 DOT off the glidepath during the final phase of the approach.
The investigation
The investigation, conducted by the operator, focused on the recurring nature of the flap transit warnings and the mechanical failures of the leading edge components. Technical personnel performed operational tests following both incidents to identify the root cause of the sensor and signal discrepancies.