WPR24LA275

The failure of the main landing gear to extend and lock for reasons that could not be determined based on the available information. Contributing to the accident was a mechanical failure of the manual landing gear release mechanism due to inadequate clearance between the release linkage and side structure and maintenance personnel’s failure to identify the interference during previous annual inspections.

The pilot was cleared for landing at the destination airport. After extending the landing gear, he performed a pre-landing check and noticed that the landing gear switch was in the down position, while the annunciator showed the gear in the retracted position. The pilot attempted to cycle the landing gear multiple times, but was unsuccessful in extending the gear. He then overflew the runway and the tower controller noted that the landing gear was only partially extended. The pilot cycled the landing gear again, attempted to shake the gear loose with abrupt maneuvers, and attempted to manually extend the gear, but remained unsuccessful. The pilot elected to land with the gear partially extended, which resulted in substantial damage to the fuselage. The landing gear was cycled multiple times during a postaccident examination, but the landing gear failure could not be reproduced. Functional testing of the manual gear extension revealed that the system did not function as designed. During tests, the gear release arm was moved in accordance with the pilot’s operating handbook instructions, yet the manual extension failed to release the landing gear. Further examination found that inadequate clearance between the push/pull rod clevis and lightening hole resulted in resistance that inhibited the release tube and torque tube from decoupling. The landing gear would manually extend when the release arm and clevis were pushed away from the lightening hole. The binding and damage to the side wall from its interaction with the push/pull rod clevis was indicative of long-term wear; however, when this interference began could not be determined based on the available information. The airplane had accrued a total of 36 flight hours in the 8 years before the accident and had received only two annual inspections during that time. Both annual inspections required a visual inspection of the side wall and push/pull clevis, which should have identified the binding between the two components.

On August 8, 2024, at about 1959 Pacific daylight time, a Piper PA-30 airplane, N8458Y, was substantially damaged when it was involved in an accident near Concord, California. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 ferry flight. According to the pilot, upon reaching the destination airport, the tower controller instructed him to report a 2-mile right base for runway 32R. He notified the tower that he was on a 3-mile right base and then extended the landing gear. After receiving landing clearance, the pilot turned onto final approach and completed a before-landing check. He noted that the landing gear switch was in the down position; however, the corresponding annunciator showed the gear in the retracted position. The pilot attempted to recycle the landing gear, but the landing gear annunciator light still indicated that the gear was retracted. The pilot conducted a go-around, but his second attempt to cycle the gear was unsuccessful. He then overflew the runway and the tower controller confirmed that the landing gear was partially down and did not appear to be locked. The pilot briefly checked the circuit breakers with his hand and noted that none had tripped. During this time, he continued to circle the airport above traffic pattern altitude while he cycled the gear multiple times and tried to shake the gear loose by turning abruptly. After these unsuccessful attempts, a mechanic and the owner of the airplane were allowed to enter the tower to help troubleshoot the failure. At their suggestion, the pilot raised the jackscrew lock to manually release the landing gear but was unsuccessful. After attempting several additional maneuvers (rolling, climbing, diving) to lower the landing gear, the tower controller noted that the sun was going down and asked if he wanted to continue. The pilot decided that he should land as he was mentally and physically worn out by his effort. The tower controller cleared the pilot to land on runway 19R, and after one more low pass the pilot landed the airplane on the partially extended landing gear. During touchdown the gear collapsed, and the airplane skidded to a stop, which resulted in substantial damage to the fuselage. Postaccident examination of the airplane revealed no preimpact mechanical anomalies with the landing gear extension and retraction system. The landing gear was cycled six times and fully retracted and extended during each cycle; no anomalies were noted with the right or main landing gear assemblies. According to the pilot’s operating manual, the airplane was equipped with an electrically-driven, retractable, tricycle landing gear system. The gear retraction was driven by a motor located in the fuselage that extended and retracted the landing gear through a gear train and actuating push-pull cables attached to each of the main landing gear and a tube in the nose gear. The emergency landing gear extension procedure contained in the pilot’s operating handbook for the airplane stated that the gear motor should be disengaged by raising the release arm and pushing it forward through its full travel. The gear extension handle, normally stored in the manual extension compartment between the pilot seats, should be placed in the left or right socket and twisted clockwise to lock in place. The handle should then be rotated full travel to extend the landing gear. The green light on the panel indicates if the landing gear is down and locked. The procedure contained three notes: 1. Do not retract with handle in slot. 2. Do not re-engage motor in flight. 3. Reducing power and rocking the gear extension handle will aid in manually extending the landing gear. Postaccident examination noted that the forward movement of the release arm was required to decouple the gear motor release arm assembly from the torque tube, which would allow the landing gear to fall (see figure 1). During the postaccident testing, the release arm was pulled upward and forward, consistent with the manual instructions; however, the landing gear would not manually release until the release arm was pushed to the right side, which was met with significant resistance. This occurred repeatedly during three separate attempts to manually extend the landing gear. Visual inspection of the manual extension system revealed that the push/pull rod clevis was binding against a longeron on the left side structure that housed the manual extension system (see figure 2). During tests, when the manual release arm was pulled up and pushed forward, the lightening hole prevented the bolt on the left side of the push/pull rod clevis from its full travel and the torque tube from rotating. When the release arm was pushed to the right, the bolt was liberated from the hole, allowing the gear retraction motor release arm and torque tube to decouple and the landing gear to fall. The binding and damage to the circumference of the lightening hole were consistent with long-term wear. Figure 1: Gear retraction motor release arm assembly, gear motor, and torque tube Figure 2: Manual extension system in gear up position with scoring on the longeron at damage signature along diameter of lightening hole The airplane’s most recent work order showed that it had accumulated a total of 18 flight hours since its most recent annual inspection, which was completed between August 5, 2022, and February 1, 2023. No corresponding logbook endorsement was entered into the aircraft logbooks. The airplane’s previous annual inspection was undated, and was completed at the same tachometer time as a separate inspection dated September 26, 2018. The previous annual inspection was completed 36 flight hours before the accident, at which time a new landing gear motor and a new up-limit switch were installed. A review of the airplane’s logbooks from 2011 to the last entry in 2023 did not contain any remarks about the manual gear extension. The two most recent annual inspection logbook entries noted that the inspections were completed in accordance with 14 CFR Part 43 Appendix D, which requires an inspection of: o All units – for poor condition and insecurity of attachment o Linkages, trusses, and members - for undue or excessive wear fatigue, and distortion.