What happened
On February 1, 2021, a Bombardier DHC-8-402, registration SP-EQC, was operating a scheduled passenger flight from Gdańsk (EPGD) to Warsaw (EPMA). Shortly after takeoff, the pilot attempted to retract the landing gear by moving the lever to the "UP" position. This action triggered several warning indicators, including the loss of three green landing gear lights, the illumination of three red lights, and a "WT ON WHEELS" (weight on wheels) alert. Despite the command, the landing gear remained in the extended position.
The flight crew performed the required checklists for this specific emergency. Upon returning the gear lever to the "DOWN" position, the three green lights immediately illuminated, indicating the gear was properly locked. After evaluating the weather conditions, which were favorable with no icing, and confirming an additional 800 kg of fuel was available, the crew consulted with the purser and technical support. The decision was made to continue the flight to Warsaw. The aircraft landed safely at EPWA, at which point the "WT ON WHEELS" alert ceased.
The investigation
Following the incident, technical services conducted a thorough inspection of the aircraft's landing gear system. The investigation established that the nose landing gear (NLG) strut, which was unweighted, was not extending to its full range. This incomplete extension caused the proximity sensor to transmit an erroneous signal, falsely indicating that weight was still present on the nose gear during flight. This incorrect signal prevented the Proximity Sensor Electronic Unit (PSEU) from initiating the landing gear retraction sequence.
Findings
- The primary cause of the incident was the incomplete extension of the unweighted nose landing gear strut following takeoff, which prevented the landing gear retraction sequence from starting.
- The faulty sensor signal created a false "weight on wheels" condition during flight.