What happened
On February 21, 2018, a Bombardier DHC-8-402 was performing a scheduled flight from Warsaw (EPWA) to Riga (EVRA). At approximately 22:40 UTC, shortly after takeoff, the crew initiated the landing gear retraction sequence. During the transition phase, the cockpit indicators malfunctioned: the nose gear light turned red, and the main gear lights extinguished. After a brief period, an amber warning light for the nose gear door opening illuminated, followed by the successful retraction of the gear after several seconds.
Concerned by the irregular indications, the crew suspended their climb and contacted Maintenance Control Center (MCC). Following consultation, the crew attempted to extend the landing gear in flight to verify the system's status. During this attempt, the nose gear locked into position correctly but took approximately 20 seconds to fully extend. Due to the ongoing technical uncertainty, the crew decided to return to Warsaw (EPWA), where the aircraft landed without further incident.
The investigation
The investigation focused on the mechanical behavior of the landing gear doors and the associated cockpit warning lights. The PKBWL examined the sequence of the gear retraction and the subsequent extension attempt to identify the source of the erroneous sensor feedback.
Findings
- The primary cause of the landing gear malfunction was a faulty proximity sensor (NGDCRCL PROXIMITY SENSOR P/N: 401020101) located within the nose landing gear door opening/closing mechanism.