Accident Sequence
During an earlier landing on a 5,008-ft-long grooved asphalt runway, the flight crew had normal braking. Later that day, the same crew departed on an executive flight with a flight attendant, the airplane owner, and five passengers. The pilot-in-command (PIC) flew a visual approach to a dry 5,000-ft runway at Vref plus 4 or 5 knots with flaps fully extended. The touchdown was described as "firm" and occurred between 300 and 500 ft beyond the aiming point marking.
After touchdown, the PIC unsuccessfully attempted to deploy ground spoilers. He applied moderate brake pressure when the nose landing gear contacted the runway but felt no deceleration. Attempts to deploy thrust reversers also failed. The PIC informed the second-in-command (SIC) of no braking energy, released the brakes, and turned off the antiskid system. He then reapplied heavy braking without deceleration and again tried thrust reversers without success. Directional control was maintained using nosewheel steering and manual brake modulation, but the airplane did not slow as expected. Approaching the runway end, the PIC intentionally veered right to avoid water ahead. The airplane exited onto sand, the nose landing gear collapsed, and it came to rest about 250 ft past the departure end.
Passengers exited, and airport personnel rendered assistance. The airplane owner, who had left his seat and moved toward the cabin door when he realized the airplane would not stop, sustained serious injuries.
Examination Findings
Postaccident examination revealed minimal pressure at the No. 2 (left inboard) brake due to a failed spring in the upper brake control valve (BCV). The coupling subassembly of the No. 1 wheel speed sensor (WSS) was fractured. A manufacturer representative stated that during brake system certification, the BCV spring failure was considered acceptably low and would be evident to flight crews within five landings. Because the airplane did not pull during braking on the earlier landing, the spring likely failed during the accident landing.
Ground spoilers and thrust reversers functioned normally during the earlier landing and postaccident testing; no malfunctions were found. The weight-on-wheels system also showed no failures. The PIC's unsuccessful deployment attempts were likely due to errors while multitasking when faced with an unexpected situation (inadequate deceleration) with little runway remaining.
Stopping distance calculations using the airplane's reported weight, weather, Vref speed, flap setting, estimated touchdown point (300–500 ft beyond aiming point, corroborated by camera footage), and assuming nonuse of ground spoilers and thrust reversers, operational antiskid and steering, and loss of one brake per side showed the airplane would have required 690 ft of additional runway. With thrust reversers used, it would still have required 27 ft of additional runway.
The PIC switched off the antiskid system despite no failure annunciations, which led to rupture of tires Nos. 1, 3, and 4 and likely fractured the No. 1 WSS coupling, further reducing braking action. The combination of the BCV spring failure, WSS coupling fracture, improper touchdown point, slightly excess speed, and subsequent tire failures resulted in insufficient runway to avoid overrun. The BCV manufacturer reported one previous BCV spring failure and 43 instances of relaxed springs, though none would have been detected without a focused inspection.
Probable Cause
The failure of a spring inside the No. 2 brake's upper brake control valve and the fracture of the coupling subassembly of the No. 1 wheel speed sensor during landing, which resulted in the loss of braking action, and the pilot-in-command's (PIC) deactivation of the antiskid system even though there were no antiskid failure annunciations, which resulted in the rupture of the Nos. 1, 3, and 4 tires, further loss of braking action, and subsequent landing overrun. Contributing to accident were the PIC's improper landing flare, which resulted in landing several hundred feet beyond the aiming point marking, and his unsuccessful attempts to deploy the thrust reversers for reasons that could not be determined because postaccident operational testing did not reveal any anomalies that would have precluded normal operation. Contributing to the passenger's injury was his leaving his seat intentionally while the airplane was in motion.