What happened
On May 5, 2015, an Embraer 170 operated by PLL LOT experienced a technical malfunction shortly after departing from Warsaw Chopin Airport (EPWA). During the takeoff phase, the flight crew found that the landing gear lever could not be moved to the "UP" position. The crew notified Air Traffic Control of their intention to return to the departure airport but did not declare an emergency. Following the execution of the "GEAR LEVER CANNOT BE MOVED UP" checklist and specific procedures regarding the Weight on Wheel (WOW) system failure, the aircraft performed a safe landing on runway 15 at Warsaw.
The investigation
The investigation examined the maintenance history of the aircraft, specifically focusing on recent modifications and repairs. Records showed that during a maintenance check on January 22–23, 2015, an Engineering Order was implemented to replace the Proximity Sensor Electronic Module with a new, modified version intended to reduce "LG NO DISPATCH" error messages.
Analysis of the Fault History Database revealed that "LG NO DISPATCH" messages had been appearing on the aircraft since January 22, 2015, even during the maintenance period. In an attempt to resolve the recurring issue, maintenance personnel replaced several components, including the CTR LEVER LANDING GEAR, the LDG SELECTOR VALVE, and the SPDA1 LRM13 MODULE. Following the incident, the aircraft was withdrawn from service, and the SPDA1 LRM13 (DC POWER MODULE) and the EMERGENCY EXTENSION OVERRIDE SWITCH were replaced. While subsequent tests were successful, the investigation noted that a similar failure had occurred on February 7, 2015, which led to the replacement of the Proximity Sensor Electronic Module No 2.
Findings
- The primary cause of the incident was a malfunction of the Proximity Sensor Electronic Module, which had been installed on January 22, 2015, as part of a modification process.
- Recurring electrical fault messages had been documented on the aircraft for several months prior to the event.