What happened
On December 2, 2014, a Bombardier DHC-8-400 operated by Eurolot SA was taxiing at Warsaw Chopin Airport (EPWA) when the crew observed a sudden, spontaneous change in the nose gear steering angle. The crew noted that the nose gear steering handle was moving on its own, exhibiting a "hunting" motion without any input from the pilot. In response to this malfunction, the crew returned the aircraft to the stand and requested technical assistance.
The investigation
Technical personnel inspected the aircraft and determined that the steering control handle was malfunctioning. To resolve the issue, the steering handle was removed and replaced with a unit from another aircraft. Following the replacement, the steering system underwent comprehensive testing. After the tests yielded positive results, the aircraft was cleared to return to service.
Findings
- The investigation identified that the internal spring within the nose gear steering mechanism had been improperly lubricated.
- This improper lubrication caused the spring to become excessively stiff.
- The stiffness of the spring resulted in the displacement of the potentiometer's output limits for left and right steering handle rotation.