What happened
On August 13, 2010, a Dassault Aviation Mystere Falcon 50, registration F-HAIR, was performing a flight inspection to support the issuance of an Air Operator Certificate (AOC) at Paris Le Bourget. The flight crew, which included a pilot inspector and a mechanic, was conducting the final leg of a series of check flights.
During the approach to runway 27, the crew identified that the anti-skid system for the left main gear was inoperative. Following established procedures, the commander selected the backup braking system. Upon touchdown at approximately 108 knots, the aircraft initially began to veer to the right. The pilot flying attempted to correct the deviation using the rudder, but the aircraft then swung sharply to the left.
As the pilot in command attempted to apply the brakes to regain control, the aircraft'ed deviated further, eventually exiting the runway to the left at approximately 55 knots. The aircraft traveled roughly 80 meters across the grass before returning to the runway surface and coming to a stop. There were no injuries to the four occupants on board.
The investigation
The BEA investigation focused on the braking performance and the maintenance history of the aircraft. Investigators examined the hydraulic systems and discovered that two hydraulic lines within the backup braking system had been reversed. This error occurred following unscheduled maintenance work performed between October 2009 and March 2010, which involved the removal and reinstallation of lines during a nose gear reaming process.
Technical documentation was reviewed, revealing that while the maintenance was performed to address a specific technical instruction, the documentation did not adequately link the specialized machining task to the subsequent reassembly and verification requirements for the hydraulic lines. Furthermore, the investigation found that the hydraulic lines lacked any permanent distinguishing marks or error-proofing mechanisms to prevent incorrect installation.
Findings
- The primary cause of the accident was the unidentified reversal of two hydraulic lines in the backup braking system following maintenance.
- The lack of physical differentiation between the two lines made the error difficult to detect during visual inspections.
- Maintenance documentation for non-scheduled tasks was incomplete, failing to specify the necessary verification steps for reassembling the hydraulic lines.
- The crew's initial observation of handling difficulties during a previous taxiing segment was not fully addressed by the commander during the landing phase.