Narrative:A G150 corporate jet, N480JJ, sustained substantial damage in a runway excursion accident at Key West International Airport, FL (EYW). One passenger sustained serious injuries.
The flight departed from Stuart-Witham Field, FL (SUA) at 19:00. Visual meteorological conditions prevailed and an instrument flight rules (IFR), flight plan was filed.
The main landing gear touched down about 1,650 feet beyond the approach end of the runway. The nosegear then touched down 2.4 seconds later and about 2,120 feet beyond the approach end of the runway, with about 2,680 feet of runway remaining.
The pilot in command stated that he then applied the brakes but thought they were not working; he had not yet activated the thrust reversers. He alerted the second in command, who also depressed the brake pedals with no apparent results. The PIC suggested a go-around and advanced the power levers from the idle position to the takeoff position. The second in command said it was too late, and the power levers were then returned to the idle position 6 seconds later. The power levers were moved to the reverse thrust position 8 seconds after that and remained in that position for the duration of the accident sequence; both thrust reversers deployed when commanded. During landing rollout the airplane departed the runway, crossed a 600-foot overrun, impacted the far side of a ditch, crossed a dirt road, cleared another ditch, and came to a stop 820 feet from the departure end of the runway.
Although armed, the airbrakes did not deploy upon touchdown; the data available was inconclusive to determine what position the throttles were in at touchdown and why the airbrakes did not deploy. It is likely that the pilots did not detect the wheel braking because its effect was less than expected with the airplane at full power and with the airbrakes stowed.
PROBABLE CAUSE: "The pilot in command's failure to follow the normal landing procedures (placing engines into reverse thrust first and then brake), his delayed decision to continue the landing or go-around, and the flight crew's failure to follow emergency procedures once a perceived loss of brakes occurred. Contributing to the seriousness of the passenger's injury was the improper securing of the passenger seat by maintenance personnel."