Newport News, VA, USA
N80PG
GATES LEAR JET 35
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.
HISTORY OF FLIGHTOn May 12, 2015, about 1144 eastern daylight time, a Gates Lear Jet 35, N80PG, call sign "Riptide 80", operated by Phoenix Air Group Inc. was substantially damaged during landing rollout, following a return to the airport after an unsafe nose landing gear indication at Newport News/Williamsburg International Airport (PHF), Newport News, Virginia. The airline transport certificated pilot and airline transport certificated copilot were not injured. Visual meteorological conditions prevailed, and an IFR flight plan had been filed for the public use flight contracted by the United States Navy, that departed PHF around 1115. According to the flight crew, prior to departure at PHF, they preflighted the airplane and found everything to be normal including the nose gear strut and oleo gear extensions. On this flight the copilot was flying from the left seat and the pilot was flying from the right seat. They taxied to runway 25 and took off about 1115 without incident. The flight crew started running the after-takeoff checklist and at "positive rate", the pilot moved the landing gear selector handle to the up position, and when he did, they felt and heard a loud "clank" come from the nose of the airplane. They also observed that the red unsafe nose gear light had illuminated. The flight crew then recycled the landing gear handle with the same result. The flight crew elected to return to PHF because of the nose gear issue. They jettisoned fuel to get below maximum landing weight and then returned to the airport for landing. The pilot asked the air traffic controller in the control tower for permission to do a low approach to runway 20, and to visually inspect their nosewheel to make sure it was not in any other position than "straight." The flight crew then selected the landing gear handle to the down position and received three green landing gear down indications (everything normal) and completed the before landing checklist. The flight crew executed a low approach for runway 20 and the air traffic controller advised that the nose landing gear appeared to be straight. The flight crew then kept the airplane in the landing configuration and entered a left downwind for runway 25. During the landing, they touched down main wheels first, and held the nose off for as long as possible. Once the nose wheel touched down and weight was on the nose landing gear, the airplane suddenly turned sharply, 30° to 40° to the left. Both flight crewmembers then applied right rudder to counter the turn without effect. The airplane then partially traveled off the left side of the runway pavement and struck a concrete runway edge-light base, with its left main landing gear, turned about 180° from its original direction of travel, and came to rest on the left side of the runway, about 1,500ft from the end. The pilot then instructed the copilot to open the main door to egress but the copilot was unable to get the door to open, so he removed the emergency exit window on the right rear side of the cabin. The pilot then completed the emergency evacuation procedures and egressed from the airplane after the copilot had egressed. PERSONNEL INFORMATIONPilot According to Federal Aviation Administration (FAA) and pilot records, the pilot held an airline transport pilot certificate with a rating for airplane multi-engine land, and commercial privileges for airplane single-engine land. He also held a flight instructor certificate with ratings for airplane single, and multi-engine, and instrument airplane, as well as type ratings for the CL-65, G-159, LR-45, and LR-JET His most recent FAA first-class medical certificate was issued on October 23, 2014. He reported that he had accrued 4,800 total hours of flight experience, 2,300 of which was in the accident airplane make and model. Copilot According to FAA and pilot records, the Copilot held an airline transport pilot certificate with a rating for airplane multi-engine land, and commercial privileges for airplane single-engine land. He also held a flight instructor certificate with ratings for airplane single engine, and instrument airplane, as well as type ratings for the A-300, B-737, B-757, B-767, CE-500, DC-9, and LR-JET. His most recent FAA first-class medical certificate was issued on November 24, 2014. He reported that he had accrued 22,542 total hours of flight experience, 1,867 of which was in the accident airplane make and model. AIRCRAFT INFORMATIONThe accident airplane was a pressurized, turbofan powered, low wing monoplane, of conventional metal construction. The swept-back wings and tail surfaces were fully cantilevered. The wing was an 8-spar, wet wing design with large external fuel tanks at the tips. The spars were continuous from tip to tip (except for Spar 6 which only extended from the landing gear ribs outboard) with all loads transferred to the fuselage through four fittings on each side. It was a derivative of wings used on previous Learjet models, with the most noticeable differences being the wing tip extensions and internal modifications, incorporated to accommodate the increased gross weight of the Model 35. It was powered by two aft fuselage mounted Garrett TFE 731-2-2B, twin spool, turbofan engines, each rated at 3,500 pounds of thrust. It was equipped with a fully retractable tricycle type landing gear with dual wheels, an anti-skid braking system, and a steerable nose wheel. Engine driven hydraulic pumps provided power for extending and retracting the landing gear, wing flaps, and spoilers. The ailerons, elevators, and rudder were manually controlled by utilizing conventional cables, bell cranks, pulleys, and push-pull tubes. The airplane could be operated at speeds of up to .81 Mach and altitudes of up to 41,000 ft, and it had been modified from its original configuration by the installation of hardpoints under each wing, along with cabling which had been installed from inside the airplane's pressurized fuselage through the pressure vessel, and out to the hard points, enabling the airplane to carry external pods or other array. According to FAA and airplane maintenance records, the accident airplane was manufactured in 1976. Its restricted category special airworthiness certificate was issued on April 1, 1996. The airplane's most recent continuous airworthiness inspection was completed on January 18, 2015. At the time of the accident, the airplane had accrued about 11,850.5 total hours of operation. METEOROLOGICAL INFORMATIONThe recorded weather at PHF, at 1154, approximately 10 minutes after the accident, included: winds 250 at 11 knots, 10 miles visibility, clear skies, temperature 31° C, dew point 21° C, and an altimeter setting of 30.02 inches of mercury. AIRPORT INFORMATIONThe accident airplane was a pressurized, turbofan powered, low wing monoplane, of conventional metal construction. The swept-back wings and tail surfaces were fully cantilevered. The wing was an 8-spar, wet wing design with large external fuel tanks at the tips. The spars were continuous from tip to tip (except for Spar 6 which only extended from the landing gear ribs outboard) with all loads transferred to the fuselage through four fittings on each side. It was a derivative of wings used on previous Learjet models, with the most noticeable differences being the wing tip extensions and internal modifications, incorporated to accommodate the increased gross weight of the Model 35. It was powered by two aft fuselage mounted Garrett TFE 731-2-2B, twin spool, turbofan engines, each rated at 3,500 pounds of thrust. It was equipped with a fully retractable tricycle type landing gear with dual wheels, an anti-skid braking system, and a steerable nose wheel. Engine driven hydraulic pumps provided power for extending and retracting the landing gear, wing flaps, and spoilers. The ailerons, elevators, and rudder were manually controlled by utilizing conventional cables, bell cranks, pulleys, and push-pull tubes. The airplane could be operated at speeds of up to .81 Mach and altitudes of up to 41,000 ft, and it had been modified from its original configuration by the installation of hardpoints under each wing, along with cabling which had been installed from inside the airplane's pressurized fuselage through the pressure vessel, and out to the hard points, enabling the airplane to carry external pods or other array. According to FAA and airplane maintenance records, the accident airplane was manufactured in 1976. Its restricted category special airworthiness certificate was issued on April 1, 1996. The airplane's most recent continuous airworthiness inspection was completed on January 18, 2015. At the time of the accident, the airplane had accrued about 11,850.5 total hours of operation. WRECKAGE AND IMPACT INFORMATIONExamination of the airplane revealed that the airplane's wing structure had been substantially damaged when the lower portion of the left main landing gear shock strut separated, the landing gear forward trunnion was torn out from its mounting location on Spar 5, and the actuator tore through the pillar in the wing structure, when the left main landing gear struck the concrete runway edge-light base. The right main landing gear then collapsed in the opposite direction of its normal direction of retraction (outward instead of inward). Further examination also revealed that the fuselage had been damaged in numerous areas along with the wing leading edges, and a mission pod which was mounted under the left wing, and both the left-wing and right-wing integral wet wing tanks had been punctured by the landing gear, resulting in a fuel spill of about 600 gallons. Examination of the nose landing gear assembly revealed that it was fully intact, the nose wheel tire was intact, undamaged, and inflated, and though covered in mud, the nose landing gear up lock mechanism was intact. The nose landing gear actuator was also fully extended in the down and locked position, and when electrical power was supplied to the airplane, a green down and locked indication was observed in the cockpit. Further examination revealed however, that the oleo strut was fully compressed, and black scuff marks existed on both the left and right walls of the nose wheel well above the door hinges, consistent with the nose wheel tire not being centered during retraction. Examination of the cockpit revealed that the circuit breaker for the terrain avoidance warning system (TAWS) which was installed to help prevent inadvertent flight into terrain was "out" (deactivated) and not collared, and the landing gear warning/mute test switch had a rubber band looped around it and the pressurization rate knob, which kept the landing gear/mute test switch in the mute position deactivating the landing gear warning horn. Examination of the cabin revealed that the cabin was filled with unsecured equipment including a cooler, engine covers, electronic equipment, and miscellaneous items that had been thrown forward during the accident sequence. There were two means of egress, the cabin door, which was located on the forward left side of the cabin just behind the cockpit, and an emergency exit window that was located on the aft right side of the cabin. The cabin door was 36" wide and consisted of an upper portion that formed a canopy when open and a lower portion with integral entrance steps. The upper portion had two torsion bars to provide opening assistance. The torsion bars had an over center design to retain the upper door in the open position. The lower door had cables at each end that were attached to spring-loaded takeup reels to aid closing and prevent damage if the door was inadvertently dropped. A safety catch would hold the lower door half in place while the upper door half was being raised. Hinged arms provided travel limit for the lower door. These arms were attached to a torsion bar to provide additional aid when closing the lower door. Each door half had a locking handle that when rotated, drove a series of pins into the fuselage structure and through interlocking arms that secured the door halves together. When locked, the door would become a rigid structural member. A 28-vdc actuator in the lower door half operated hooks that pulled the doors together against the door opening perimeter seal. This must be done before the locking pins would engage. According to the Pilot's Manual, the hooks must be released after the locking pins were engaged or the DOOR warning light in the readout panel would illuminate. Switches in the pin sockets would also energize the warning light if the pins were not fully engaged. Examination of the main cabin door revealed that door hooks were still engaged, but no anomalies, with either the door latching mechanism, or door indication system, that would have precluded indication of the DOOR warning light or hampered egress was discovered. Both upper and lower door levers could be operated without issue, and the upper and lower doors were able to be opened and closed normally. When electrical power was applied to the airplane, the DOOR annunciator light would also extinguish when the hooks were fully cycled. Examination of the emergency exit window revealed that it was equipped with external and internal handles, it was functional, and that it opened without issue when the flight crew had egressed. ADDITIONAL INFORMATIONAnother Occurrence On April 28, 2016, Phoenix Air Group advised the NTSB that during routine maintenance, they identified another airplane with a steering anomaly while conducting routine maintenance on a Learjet 36A. During the maintenance procedures it was identified that the nose wheel strut appeared to be underserviced and when jacking up the airplane (with the electrical power turned on) the nose landing gear turned to the left. After recognizing that the behavior was similar to what occurred on the accident flight and previous testing, maintenance personnel removed the top off the steering servo, and found that it was contaminated with hydraulic fluid from the strut leaking internally. Review of Manufacturer's Guidance. Review of the LearAvia Steering Systems Nose Wheel Steering Actuator Maintenance Manual and Bombardier Learjet's FAA approved inspection program revealed that no recommended scheduled overhaul requirement for the steering servo was listed. Corrective Actions In order to increase safety, the parties to the investigation took the following actions: Phoenix Air Group - On February 26, 2016, Phoenix Air Group stressed to their maintenance department and line personnel, that strut servicing and nose gear extension on preflight is critical and must be watched continuously on every airplane prior to launch. - On April 22, 2016, as part of their 14 CFR Part 135 annual training, Phoenix Air Group advised their flight crews that deactivation of required safety systems such as TAWS and the landing gear warning horn were not acceptable and that loose gear needed to be netted or strapped down for flight. This was reiterated to their flight crews via an email from the director of operations on April 28, 2016, which included images from the investigation which emphasized the areas of concern. Bombardier Learjet The strut of the nose landing gear on the accident airplane was equipped with a P/N 2342107-001 upper seal retainer ring. Bombardier found that P/N 2342107-001 upper seal retainer rings could allow air to pass beyond the upper seal under certain conditions and that an available improved P/N 2342107-003 seal retainer ring could reduce the likelihood of this occurring. As a result, for all Learjet aircraft on which P/N 2342107-001 seal retainer rings were used, Bombardier modified the Illustrated Parts Catalog (IPC) to add the P/N 2342107-003 seal retainer ring as a spare and modified the applicable maintenance/service manuals to have the retainer ring added to the list of parts replaced at overhaul, to ensure that the upper seal retainer ring is upgraded during all overhauls, resulting in the elimination of the P/N 2342107-001 seal retainer ring by attrition over time. With regards to the LearAvia steering servo, for all Learjet aircraft which use this equipment, Bombardier introduced a 2,400 hour or "
The flight crew’s inadequate preflight inspection of the nose landing gear strut, which resulted in the nosewheel not being aligned during retraction and the subsequent loss of directional control. Contributing to the accident was the failure of the nose landing gear strut due to inadequate pressure and excessive wear.
Source: NTSB Aviation Accident Database
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