ERA15LA212

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.

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.

Narrative communications place holder Narrative damage to aircraft place holder Narrative fire place holder As the airplane had been modified to a configuration that had fewer than 6 passenger seats, a cockpit voice recorder (CVR) was not required under Title 14 Code of Federal Regulations Parts 91 or 135. Examination of the airplane revealed though, that a Fairchild A-100 CVR system was installed. According to FAA records, the CVR was installed through a Supplemental Type Certificate (STC) in February 1991. This model CVR, would record a minimum of 30 minutes of analog audio on a continuous loop tape in a four-channel format: one channel for each flight crew, one channel for a cockpit observer, and one channel for the cockpit area microphone (CAM). The A-100 was equipped with test functionality to assist pilots in determining that the CVR was functioning. When the test is initiated, a tone is recorded to each channel of the CVR and subsequently detected by the monitor head and played back through a headset jack in the CVR control panel. The tones would also trigger a test meter for a visual indication that the test was successful. According to the STC documentation, an inertial, or "G" switch, was installed as part of the CVR installation. A "G" switch is designed to remove power from the flight recorders upon detection of an acceleration that reaches a certain factory preset threshold in order to prevent flight recorder information from being overwritten. The switch would be triggered when it sensed a 3 G acceleration along a single axis. The switch could be reset using a button on the unit, which would restore CVR functionality. Examination of the CVR revealed that it had not sustained any heat or structural damage and the audio information was able to be extracted from the recorder normally. The tape compartment inside the crash protected portion of the CVR was clean and was not contaminated with debris or tape filings. When 28 volts DC was applied to the CVR through an inverter, the tape transport drive functioned normally. Maintenance records indicated that, the underwater locator beacon battery was replaced on January 22, 2015, and a decal inside the insulation assembly of the CVR indicated that the last maintenance that had been performed internally on the unit itself, occurred as early as July 2009. Typically, during maintenance, the audio would be bulk erased, and a test would be performed prior to returning the unit to service. Review of the recording revealed that none of the audio was pertinent to the accident investigation, and the audio contained indications that the tape had been bulk erased. Test tones were also present on each channel near the end of the tape. Narrative injuries to persons place holder Phoenix Air Group Inc. held a 14 CFR Part 135 certificate with worldwide operating authority. They were headquartered at Cartersville-Bartow County Airport (VPC), Cartersville, Georgia. They provided passenger services, air ambulance services, air cargo services, and contracted airborne electronic warfare and weapons training/testing services. Phoenix Air's maintenance, dispatch operations and headquarters staff were all located at VPC, and all "heavy" airplane maintenance and airplane modifications were also performed at VPC. They also ran a fixed base operation as well as a flight school at VPC, and had offices, airplanes, and staff in several states, and around the world, where company airplanes and personnel were supporting various long-term contracts. At the time of the accident Phoenix Air operated 13 Learjets, in addition to other multiple airplane types in their fleet. Narrative other damage place holder Narrative survival aspects place holder Narrative useful or effective investigation techniques place holder PHF was owned by the Peninsula Airport Commission and was a public use, tower controlled airport. It was located nine miles northwest of Newport News, Virginia. The airport elevation was 42 ft above mean sea level. There were two runways oriented in an 2/20 and 7/25 configuration. Runway 25, had a left-hand traffic pattern, was asphalt, grooved, and in good condition. The total length was 8,003 feet-long and 150 feet-wide. It was marked with precision markings in good condition and equipped with high intensity runway edge lights. A 4-light precision approach path indicator was located on the left side of the runway which provided a 3.00° glide path to touchdown. It was also equipped with runway end identifier lights and an ILS/DME instrument approach. Obstructions were present off the approach end of the runway in the form of 41 ft trees, located 1,100 ft from the runway, which took a 21:1 slope to clear. Examination of runway 25 revealed the presence of tire marks that matched the geometry of the airplane's right main, and nose landing gear which led off the left side of the paved surface of the runway to a damaged runway-edge light, and from the runway edge light back up on to the paved surface of the runway. Nose Landing Gear and Nose Wheel Steering The nose landing gear consisted of the nose wheel and chined tire mounted on a conventional air/hydraulic shock strut which was housed in, and attached to, the fuselage structure by bearing plates. The nose landing gear strut used its internal gas pressure to fully extend the strut at take-off. When fully extended, the centering cams inside the strut would engage and ensure that the lower portion of the strut assembly and nose wheel were aligned straight ahead. The nose gear strut and the nose wheel bay were designed in such a way, that the nose wheel must be aligned straight ahead, for the wheel to go into the narrow bay. In addition, the uplock hook assembly would connect to a pin which was on the lower strut. Therefore, if the strut was not fully extended, even if it was aligned straight ahead, the uplock would not engage. The variable authority nose wheel steering was electronically controlled by the rudder pedals through a system of switches, relays, a computer-amplifier, follow-ups, and a servo. Nose wheel travel was inversely proportional to ground speed: i.e., from zero to 10 knots, 45° degrees of nose wheel steering was available, decreasing to 8° at 45 knots. The system used the left inboard, right outboard and right inboard wheel speed transducers to provide input signals to the computer-amplifier, and rudder pedal movement would drive the rudder pedal follow-up which would apply a voltage displacement signal to the input of the nose-steering computer-amplifier. The computer-amplifier would apply a clockwise or counter-clockwise signal to the steering actuator. This signal application would cause the actuator clutch to engage the actuator motor. The clutch output torque would drive the actuator gear train and position the nose wheel to the related position. The nose wheel steering system was controlled by the Nose Steering switch on the control wheels or by depressing the STEER LOCK switch. The STEER ON light on the glare shield would come on when the nose wheel steering was on. STEER LOCK was released by pressing the control wheel Nose Steering Switch. After recovery of the airplane from runway 25, the airplane was moved to a parking ramp where field testing of the functionality of the nose landing gear and nose wheel steering was conducted. The testing was performed after servicing of the nose landing gear shock strut per Chapter 12-10-03, of the Learjet Maintenance Manual. During servicing for the testing, only one ounce of hydraulic fluid was required to fully service the strut which indicated that the strut was nearly full of fluid when the accident occurred. The strut however was found to be devoid of nitrogen. Prior to servicing the strut with nitrogen, the nose wheel was turned 40° to the left to see if it would center after servicing. Then as outlined in