Accident Learjet 35A N22MS,

ASN Wikibase Occurrence # 320764

Date:	Monday 13 May 2013
Time:	12:45
Type:	Learjet 35A
Owner/operator:	Evergreen International Aviation
Registration:	N22MS
MSN:	35A-209
Year of manufacture:	1978
Total airframe hrs:	15047 hours
Cycles:	9491 flights
Engine model:	Garrett TFE731-2-2B
Fatalities:	Fatalities: 0 / Occupants: 3
Aircraft damage:	Substantial, written off
Category:	Accident
Location:	McMinnville Municipal Airport, OR - United States of America
Phase:	Landing
Nature:	Ferry/positioning
Departure airport:	Grand Junction-Walker Field, CO (GJT/KGJT)
Destination airport:	McMinnville Municipal Airport, OR (KMMV)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
The aircraft, a Learjet 35A, N22MS, experienced a runway overrun upon landing at McMinnville Municipal Airport, Oregon.
The aircraft sustained substantial damage and the three passengers onboard were not injured.
The airplane had just undergone a flight management system (FMS) upgrade at a maintenance facility in Grand Junction, and this was both its first flight, and its home base return flight, following the upgrade.
The pilot reported that the flight and landing approach were uneventful. As the airplane touched down on runway 22, the pilot deployed the spoilers, and then pulled the power levers to the thrust reverser detent position; however, the deploy indicators did not illuminate. He then recycled the thrust levers back into the detent, but again the reversers did not deploy. Both the pilot and copilot attempted to troubleshoot as the airplane continued along the runway. The pilot then applied pressure to the foot pedal brakes, but did not feel a response; the copilot also attempted, but reported that the pedals felt loose and the airplane did not slow down. As the airplane approached the threshold, the pilot engaged the steering lock switch, and attempted to steer the nose wheel, but the airplane did not respond. Just prior to reaching the runway end, he activated the emergency braking lever; however, the airplane rolled off the runway end, through a set of instrument landing system antennas, and down an embankment.

Subsequent examination revealed that the mounting screws for both the left and right main landing gear squat switches were loose, such that the switches had backed away from their mounting pads.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
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 the 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, and 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.

Accident investigation: