ERA21LA138 · Dassault Aviation MIRAGE F1 B

During takeoff roll from a runway equipped with a raised aircraft arresting system, the pilot of the turbojet-powered fighter airplane noted no discrepancies upon reaching 100 knots, and before the airplane had reached a raised aircraft arresting system that was present across the runway. The takeoff roll continued and at about 125 knots, which was just after the airplane had crossed the arresting system, the airplane suddenly swerved left. As the airplane neared the left edge of the runway it became airborne. While airborne and orbiting near the airport, the front- and rear-seat pilots reviewed the applicable emergency procedure checklists, discussed possible system failures, and had pilots from another airplane provide a visual check of the accident airplane’s landing gear. Based on the information provided and the lack of an annunciation of any problem with the nosewheel steering (NWS) system, the pilots attributed the sudden swerve to an issue with the left main landing gear. Although there was some discussion about a hard over of the NWS system, the pilot left it on but planned to turn it off if the airplane veered during the emergency landing. The pilot burned fuel and returned for landing on the right side of a 200-ft-wide runway. After touchdown the airplane veered to the left, travelled off the runway and onto the grass infield, and the nose landing gear to collapsed. The rear-seat pilot initiated an unannounced ejection, which should have resulted in the front seat also ejecting; however, the rear seat ejected successfully, but the front seat did not. The airplane came to rest and both pilots sustained serious injuries. A postaccident examination of the NWS system revealed that the annular bearing of the distribution block fractured in overload, with no evidence of preimpact failure or malfunction. The fracture likely resulted from travelling over the raised aircraft arresting system at a high speed, the shock from which traveled from the nose landing gear into the distribution block and resulted in a fracture of the bearing race. Because of the fractured bearing race, the distribution block commanded a left turn consistent with the condition reported by the pilot during takeoff and landing. Although the airplane checklist for failure of the NWS did not include a loss of control during takeoff, it is likely that had the NWS been disconnected upon landing when the nosewheel touched down, directional control would have been possible using differential braking for directional control authority and the airplane likely could have been stopped safely on the runway. The postaccident examination of the front seat pilot’s ejection seat determined that it did not eject from the airplane because of impact damage to aircraft structure that secured the lower ejection seat gun mount, which resulted in movement of the seat and subsequent separation of a gas line from the rear seat to the front seat, which made ejection of the front seat impossible.

Verbatim NTSB analysis and probable cause from the NTSB dataset