Incident Overview
On April 4, 2016, a Boeing 737-400 operated by Polskie Linie Lotnicze LOT S.A. was conducting a flight into Warsaw Chopin Airport (EPWA). During the final approach phase, while extending the flaps, the flaps jammed in a position between 10 and 15 degrees. The flight crew executed a go-around, and an uncertainty phase was declared at EPWA.
Crew Actions
After the go-around, the crew contacted the Maintenance Control Center (MCC). They then deployed the flaps using the alternate extension method to the 20-degree position. Subsequently, the crew performed a normal landing, after which the uncertainty phase at EPWA was canceled. The crew submitted an Air Safety Report (ASR).
Technical Findings
The aircraft was handed over to technical services for inspection. They discovered insufficient lubrication of the flap drive mechanisms, specifically noting a lack of grease in the grease nipple. The mechanisms were lubricated in accordance with Aircraft Maintenance Manual (AMM) 12-22-715-001 REV.83, followed by a functional test per AMM 27-51-00-715-001 REV.83, which yielded satisfactory results.
Probable Cause
The probable cause of the incident was insufficient lubrication of the flap drive mechanisms, caused by a lack of grease in the grease nipple.
Preventive Actions
The operator recorded the event in its Safety Management System (SMS) database and classified it according to LOT's criteria. It will be included in aviation safety indicators (SPI) monitored under the guidelines in the Aviation Safety Management Manual.