Gates Lear Jet 35 N80PG

Before departure, the pilot and copilot completed a preflight inspection of the airplane and found everything to be normal. After taking off without incident, the flight crew started running the after-takeoff checklist and the pilot moved the landing gear selector handle to the up position. The crew then felt and heard a loud "clank" in the nose of the airplane and observed that the red or unsafe nose gear light had illuminated; recycling the landing gear handle had the same result. As the flight crew returned to the departure airport, they selected the landing gear handle to the down position and received three green landing gear down indications and completed the before landing checklist; the air traffic controller advised that the nose landing gear appeared to be straight. During the landing, the airplane touched down on the main wheels first, but once the nosewheel touched down and weight was on the nose landing gear, the airplane suddenly turned sharply 30° to 40° to the left and application of right rudder did not counter the turn. The airplane then partially traveled off the left side of the runway pavement, its left main landing gear struck a concrete runway edge-light base, then the airplane turned about 180° from its original direction of travel and came to rest on the left side of the runway about 1,500 ft from the end of the runway. The copilot was unable to open the main door to egress, so he removed the emergency exit window and the pilot and copilot egressed. The airplane sustained substantial damage to the wings and fuselage. The nose landing gear strut normally uses its internal gas pressure to fully extend at takeoff, then the centering cams inside the strut engage and ensure that the lower portion of the strut assembly and nosewheel are aligned straight ahead. The nosewheel must be aligned straight ahead for the wheel to retract into the narrow nosewheel bay. Tire marks were observed inside the wheel well at a location consistent with a strut that was not fully extended. Further, if the strut was not fully extended, the uplock hook assembly could not connect to a pin that was on the lower strut and engage. Thus, a takeoff with a deflated strut would result in the strut not having enough internal pressure to fully extend into the centering cams. Forces on the strut would then cause it to turn to the left due to the asymmetric design of the nose landing gear. The most recent nose landing gear strut service was performed about 70 hours before the accident. However, examination of the strut fluid level immediately following the accident revealed that it was slightly low and that the strut was completely collapsed and devoid of nitrogen. Examinations of the nose landing gear strut also revealed that it had likely been leaking fluid for some time before the accident; as a result of the leak, the strut was flat before the takeoff, which should have been noticeable during the preflight inspection and during taxi, and that the nose landing gear was most likely not aligned straight during retraction. Examination of the steering servo also revealed that the friction material in the servo clutch was completely worn away in the drive area, giving a metal-to-metal drive from the motor to the steering system, which produced a high residual torque condition. The high residual torque likely prevented the nosewheel from self-centering and castering during the landing, causing the nosewheel to remain in a cocked position during nose landing gear touchdown, which led to the runway departure.

Quoted verbatim from the NTSB record.