Panama City, FL, USA
N601AX
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.
HISTORY OF FLIGHTOn February 25, 2021, about 1126 central standard time, a Dassault Aviation Mirage F1B, N601AX, was substantially damaged when it was involved in an accident at Tyndall Air Force Base (PAM), Panama City, Florida. Both pilots sustained serious injuries. The airplane was operated as a public aircraft under the provisions of Title 49 of the United States Code Sections 40102 and 40125. The planned flight of the dual-seat, turbojet-powered fighter airplane was conducted under the provisions of a contract between by Airborne Tactical Advantage Company (ATAC) and the United States Air Force to provide ATAC owned and operated aircraft to support adversary training for U.S. military forces. The accident airplane was the lead of a two-airplane formation departure from runway 14R at PAM. As the lead, the accident airplane was lined up on the left side of the runway and the second airplane was lined up on the right side of the runway. The accident pilot reported that he initiated the takeoff roll with the nose gear steering selected to low. A line speed check was performed at 100 knots indicated airspeed (KIAS) and before the airplane had reached the arresting cable, located about 1,440 ft from the approach end of runway 14R. Everything was acceptable at that time. The takeoff roll continued and at about 125 KIAS, which was just after the airplane had crossed the arresting cable, the pilot reported, “there was this huge swerve to the left and it was an instantaneous swerve.” He applied full right rudder input and tapped the right brake, but without effect. The airplane drifted towards the left edge of the runway and the pilot applied aft elevator input, became airborne and flew in ground effect. The airplane accelerated and climbed while remaining in the same configuration (flaps and slats full, gear down). The pilot flew south over the water where he orbited numerous times to burn fuel and determine the condition of the airplane. The second airplane had aborted its flight during the takeoff roll. While orbiting over the water, the front- and rear-seat pilots reviewed the applicable emergency procedure checklists and discussed possible system failures, such as blown tires, brake and anti-skid failures, NWS failures, and loss of control. Nearby pilots provided a visual check of the landing gear and tires. The accident pilots’ operations base also provided input into the most likely cause of the problem. After considering all the possibilities, the consensus was that there was an issue with the left main landing gear. The pilot also stated that he was prepared to turn off the NWS if the airplane started veering after touchdown. After burning fuel and coordinating with air traffic control, the pilot returned to PAM to land on the right side of runway 14L. He touched down near the right edge of the runway. When the main landing gear contacted the runway, the rear-seat pilot deployed the airframe drag chute. The pilot put the nose down as soon as he landed and felt a significant pull to the left occurring soon after he relaxed left-wing-up control input. He applied full right rudder and brake but without effect. He did not turn off the NWS because of the rapid sequence of events. The airplane departed the runway onto the grass infield and the nosewheel landing gear collapsed. The rear-seat pilot initiated an unannounced ejection; the rear seat ejected successfully, but the front seat did not. The airplane continued to skid across the grass infield and then impacted a taxiway. When the airplane came to rest, the pilot secured the engine but was unable to get out of the airplane. Both occupants were rescued by responding emergency personnel and both had incurred serious injuries. AIRCRAFT INFORMATIONAccording to ATAC’s Mirage F1 flight manual, the airplane was equipped with electro-hydraulic nosewheel steering (NWS) that was commanded by the rudder pedals and available whenever a microswitch on the nose strut (weight-on-wheels switch) was compressed. The flight manual had a procedure for the symptom, “Aircraft Swerves During Taxi.” The action items directed the pilot to verify that the NWS caution light was out. If it was out, it specified to check the rudder trim, and if required, turn off the anti-slip switch. If that was unsuccessful, the pilot was to turn off the NWS switch. The airplane was equipped with ejection seats at both positions, capable of ejection at all altitudes and at all speeds between 0 and 620 knots. A sequence selector in the front cockpit was used to select the ejection sequence for either solo or dual flight operations In the DUAL position, both seats were connected for ejection by the ballistic manifold to the disconnecting block/disconnect unit to the airframe connection (Command Selector valve) at the front seat or Connector Unit (rear seat). If the rear cockpit initiated the ejection sequence, the rear seat ejected immediately, and the gas from the rear connector unit flowed to the front seat disconnect unit to begin the ejection sequence. A built-in 0.5 second delay occurred before the front seat ejection was initiated. Seat ejection was controlled by pulling the firing handle on the front of the seat bucket between the occupant’s thighs. At the time of the accident, neither the flight manual nor the operator had any limitation preventing operation of the airplane from a runway equipped with an aircraft arresting system. AIRPORT INFORMATIONAccording to ATAC’s Mirage F1 flight manual, the airplane was equipped with electro-hydraulic nosewheel steering (NWS) that was commanded by the rudder pedals and available whenever a microswitch on the nose strut (weight-on-wheels switch) was compressed. The flight manual had a procedure for the symptom, “Aircraft Swerves During Taxi.” The action items directed the pilot to verify that the NWS caution light was out. If it was out, it specified to check the rudder trim, and if required, turn off the anti-slip switch. If that was unsuccessful, the pilot was to turn off the NWS switch. The airplane was equipped with ejection seats at both positions, capable of ejection at all altitudes and at all speeds between 0 and 620 knots. A sequence selector in the front cockpit was used to select the ejection sequence for either solo or dual flight operations In the DUAL position, both seats were connected for ejection by the ballistic manifold to the disconnecting block/disconnect unit to the airframe connection (Command Selector valve) at the front seat or Connector Unit (rear seat). If the rear cockpit initiated the ejection sequence, the rear seat ejected immediately, and the gas from the rear connector unit flowed to the front seat disconnect unit to begin the ejection sequence. A built-in 0.5 second delay occurred before the front seat ejection was initiated. Seat ejection was controlled by pulling the firing handle on the front of the seat bucket between the occupant’s thighs. At the time of the accident, neither the flight manual nor the operator had any limitation preventing operation of the airplane from a runway equipped with an aircraft arresting system. WRECKAGE AND IMPACT INFORMATIONExamination of runway 14R was performed by representatives of the Federal Aviation Administration (FAA), the operator of the airplane, and the ejection seat manufacturer. Markings from the main and nose landing gear tires were first identified about 580 ft past the arresting system closest to the approach end of the runway. The markings were initially centered on the left side of the runway consistent with the takeoff position and appeared to swerve to the left. The marks from the main landing gear tires continued to the point where the airplane became airborne. At that location the left main landing gear was off the left side of the paved surface and the right main landing gear was left of the runway edge marking but still on paved surface. Further examination of the runway revealed damage to one runway edge light associated with the tire track from the right main landing gear. Following the accident, runway 14R was swept and the sweeper truck contained a component that was determined to be the missing anti-skid connector from the right main landing gear of the accident airplane. Examination of the landing runway, 14L, and the ground path revealed it could not be determined by physical evidence where the airplane touched down; however, based on video evidence the airplane appeared to touch down near the intersection of taxiway Delta, or about 7,000 ft before the departure end of the runway. Inspection of the runway revealed light residue from the nose landing gear tires and the marks from the nose landing gear tires showed a veer to the left. The marks from the nose and then main landing gear tires continued off the left side of the runway with the marks from the nose tires closer to the left main consistent with the airplane being yawed to the left. The marks from the tires continued onto the grass that was relatively flat except one area described as a “ramp,” or about an 18-inch rise in terrain. Immediately before the “ramp” marks in the grass were noted but no marks were noted for about 29 ft after the ramp. Either on the “ramp” or about 10 ft after the “ramp,” a section of the airplane’s floorboard or pressure bulkhead was found, while about 282 ft after the “ramp” large pieces of rear canopy were noted. The marks then continue across grass adjacent to the runway and also across taxiway Foxtrot then onto grass, where the airplane came to rest upright with the nose landing gear collapsed about 5,857 ft and 122° from the approach end of runway 14L. Examination of the airplane where it came to rest revealed the nose landing gear was collapsed aft and the anti-skid connector of the right main landing gear was separated. The drag chute was deployed and the air brakes, flaps, and slats were fully extended. The drag chute did not display any signs of scorching or damage. The cockpit rear canopy was shattered consistent with the ejection sequence, while the front cockpit canopy had a small section broken out on the rear left side. The main and nose landing gear tires were checked and all were satisfactory except the left nose tire, which registered 0 psi and exhibited tears in multiple areas. The rudder trim was set at, “0 or 30 minutes.” Examination of the front cockpit revealed the anti-skid switch was in the off position and the NWS disconnect switch was on with the guard covering the switch. The sequence unit selector valve in the front cockpit was selected to “Dual.” The front ejection seat, which did not deploy, was made safe before the airplane was recovered. Postaccident examination of the airplane following recovery was performed by representatives from the FAA, aircraft operator, and ejection seat manufacturer. Examination of the airframe revealed damage to the airframe attachment of the nose landing gear actuator, structural separation of pieces of the pressure bulkhead adjacent to the front seat lower ejection gun seat mount, and structural damage to fuselage forward of the forward edge of the forward windshield or canopy. Examination of the nose gear steering system revealed that the annular ball bearing outer race was fractured consistent with a static load, with no evidence of preimpact failure or malfunction. Testing of the NWS distribution block revealed that the nose landing gear went uncommanded “immediately” to the left 45°, which was inconsistent with switch position, rudder pedal position, and system design. According to a report from the ejection seat manufacturer representative and the operator, the airplane was travelling about 55 knots when the ejection was initiated by the rear seat occupant; the ejection was not verbalized or commanded. At that time the airplane was in a 10° nose-low attitude due to the collapsed nose landing gear. Inspection of the rear ejection seat revealed no issues. Inspection of front ejection seat by the ejection seat manufacturer representative revealed that the lower seat attachment bolt was broken and the upper seat attachment bolt was deformed; thus the seat was only secured by the upper attachment. Damage to the ejection gun window top latch was consistent with seat movement in the up direction. Further examination of the seat revealed the ballistic time release unit “sear” was dislodged from its housing and activated. That activation also released all of the pilot harness locks and the scissor link on top of the seat to release the main parachute. The disconnecting unit, which routes gas from the rear to front ejection seats to initiate ejection sequence, was disconnected from the front seat ballistic manifold. As a result of the separation, gas was discharged into the cockpit consistent with a report from the front-seat pilot. A pull test of the connections of the disconnect unit revealed no discrepancies. No other discrepancies were reported for the front ejection seat. ADDITIONAL INFORMATIONPrevious Similar Event According to the operator of the accident airplane, in May 2020 an industry competitor flying a similar make and model airplane experienced a loss of directional control during takeoff that was attributed to having traveled over a raised aircraft arresting system. The National Transportation Safety Board did not investigate the event. As a result of the event the operator of that aircraft prohibited crossing raised arresting gear systems with the nosewheels at high speed. The operator of the accident airplane was not aware of that event and that company’s policy change until after the accident. After Accident Safety Changes After the accident, the owner/operator incorporated numerous safety changes, which included an updated policy prohibiting crossing a raised aircraft arresting system at high speed, a one-time inspection of the NWS and ejection seats for their fleet of aircraft, a safety sharing information agreement with an industry competitor operating similar aircraft, and the hiring of a subject matter expert familiar with the airplane to provide operational consulting. They also modified their flight manual for ejection decisions in the event of a runway excursion, developed immediate action procedures for runway excursion, and developed procedures for a loss of directional control on landing. In addition, they made the results of the accident available to all pilots and mechanics and to all pilots during their initial training.
Nose landing gear contact with a raised aircraft arresting system during takeoff, which damaged components of the nose wheel steering system and resulted in an uncommanded left turn and loss of directional control.
Source: NTSB Aviation Accident Database
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