A 1978 built Learjet 35A was operating a post-maintenance positioning flight from Grand Junction-Walker Field ( Colorado, USA) to McMinnville Municipal Airport (Oregon, USA) on this day in aviation history in 2013. Two pilots and one passenger are on board the aircraft for the roughly 850 miles (1360 km) flight. It was the aircraft's first flight after a Flight Management System modification, as well as a ferry flight to its home base.
The aircraft in its final position, shortly before recovery (© NTSB)
The crew performed the pre-start checks after being informed, by the engineer who was to fly with them, that the required pre-flight inspections had been done. As it was the first flight after maintenance additional checks were performed and all checks were satisfactorily completed. And the aircraft set off for its home base.
After an uneventful flight, with all systems operating flawless, the aircraft approached runway 22 at McMinnville Municipal Airport. With the landing clearance issued the aircraft touched down 500 feet from the beginning of the runway. The pilot flying deployed the spoilers and pulled the thrust levers to the idle reverse position. A check of the reverser indication showed that the reversers did not deploy. The thrust levers were cycled back to forward thrust and back to the idle reverse position. To no avail, the reversers did not deploy. With approximately 2000 feet of runway remaining, the speed had dropped to ~25 knots the wheel brakes were applied. But no obvious braking response was noticed, from the captain or first officer's side.
The aircraft in its final position (source http://avclaims.com © Unknown)
The copilot then pulled the thrust lever past the deploy detent causing the engines to spool up. But since the reversers had not deployed as a result the aircraft's speed increased. The thrust levers were then placed in the idle/deploy detent. In an attempt to steer the aircraft to the left the crew noticed that the nose wheel steering was non-responsive. Just before leaving the paved surface area, the crew activate the emergency brakes. But it was too late to stop the aircraft on the runway. It went through the localiser antenna and continue down an embankment where it came to a stop.
The crew and the engineer evacuated the aircraft without injury.
The aircraft during recovery (source http://avclaims.com © Unknown)
The National Transportation Safety Board investigated the accident, and in their final report (available by clicking here) identified the following probable cause(s);
Failure of maintenance personnel to reattach the landing gear squat switches following maintenance, which rendered the airplane's steering, braking, and thrust reverser systems inoperative during landing.
Contributing to the accident were;
Failure of both the maintenance facility mechanics and the airplane operator's mechanic and flight crew to identify the error during post-maintenance checks
A failure of the airplane's pilot to apply the emergency brakes in a timely manner
The copilot's decision to attempt to engage the thrust reversers as the airplane approached the runway end despite multiple indications that they were inoperative and producing partial forward, rather than reverse, thrust.