What happened
On April 4, 2016, a Boeing 737-400 operated by PLL LOT was performing a final approach into the Warsaw Chopin Airport (EPWA) control zone. During the deployment of the flaps, the mechanism became stuck in the 10-15 degree position. Due to this malfunction, the crew executed a go-around. Following the maneuver, a state of uncertainty was declared within the EPWA CTR. The crew notified the Maintenance Control Center (MCC) and successfully utilized an alternative method to extend the flaps to the 20-degree position. The aircraft subsequently completed a normal landing, after which the state of uncertainty was lifted.
The investigation
The investigation, conducted by the operator, focused on the mechanical failure of the flap system. Technical crews inspected the aircraft following the landing and examined the flap drive mechanisms. The inspection revealed that the drive mechanisms were insufficiently lubricated. The investigation established that the lubrication failure was due to a lack of grease in the grease reservoir.
Findings
- The primary cause of the incident was insufficient lubrication of the flap control drive mechanisms.
- The lack of lubrication was directly caused by an empty grease reservoir.
- Following the discovery, maintenance personnel lubricated the mechanisms in accordance with the Aircraft Maintenance Manual (AMM) and performed successful operational tests.