What happened
On 17 January 2007, a Bombardier CRJ100ER, registration F-GRJO, was performing a commercial passenger flight from Paris to Southampton when a failure occurred in the No 3 hydraulic system. The crew became aware of a low-pressure warning approximately two minutes before landing. During the approach, the crew did not follow the specific instructions in the Quick Reference Handbook (QRH), which required the nosewheel steering and hydraulic pumps 3A and 3B to be switched off.
Upon touchdown on Runway 20, the aircraft began to deviate from the centerline. Despite the application of maximum reverse thrust and heavy braking, the aircraft experienced an uncommanded rightward steering input. The aircraft eventually left the paved surface at the junction of Taxiway Bravo, traveling 61 metres onto the grass before coming to a halt. There were no injuries among the 33 passengers or 3 crew members on board.
The investigation
The AAIB examined the aircraft's flight recorders, which revealed that the nosewheel steering remained active during the landing roll. Investigators also inspected the aircraft's hydraulic components and found a leak at the outlet of hydraulic pump 3A, caused by a ruptured O-ring and a missing locking wire.
Further engineering analysis of the nosewheel steering system demonstrated that if hydraulic pressure falls within a specific range (650 to 1,650 psi) while the steering is engaged, the nosewheels can slowly drift in one direction without pilot input. This was consistent with the observed movement of the aircraft on the runway.
Findings
- The primary cause of the excursion was uncommanded nosewheel steering resulting from the hydraulic system failure.
- The crew failed to follow the QRH procedure, which would have mitigated the steering issue by switching off the nosewheel steering and the 3A and 3B pumps.
- A ruptured O-ring and a missing locking wire at the pump 3A elbow joint led to the rapid loss of hydraulic fluid.
- The nosewheel steering system was susceptible to drifting when hydraulic pressure was depleted to a specific intermediate level.