WPR25LA122

The failure of the left main landing gear to fully extend and lock as a result of broken downlock switch wires and the failure of the pilots to complete the manual gear extension checklist.

The two pilots were performing a simulated instrument approach when they noted the nose landing gear did not indicate it had extended and locked. The pilots performed a missed approach and began to troubleshoot the issue by raising and lowering the landing gear several times, which eventually resulted in the nose and right main landing gear locking; however, the left main landing gear no longer provided a down-and-locked indication. Noting that the gear in-transit lights and warning horn were not activated, the pilots believed the failure of the left main landing gear down light to illuminate was erroneous and did not complete the landing gear manual extension checklist. During the subsequent landing, the left main landing gear collapsed and the left wing impacted the runway, resulting in substantial damage. Postaccident inspection of the airplane revealed several wires in the left main landing gear downlock switch were broken, likely as a result of snagging on the up position switch bracket while the gear was in transit. According to the airplane’s maintenance manual, when the landing gear is selected down, the airplane senses all three landing gears have fully extended and locked using downlock switches on each landing gear. Actuation of the downlock switches opens the circuits powering the landing gear hydraulic pump and in-transit lights, and closes the circuit to the green gear down lights. Labels on the broken downlock switch wires corresponded to the circuits that provide electrical power to the landing gear hydraulic pump and red in-transit lights. The airplane was lifted on jacks and the landing gear was cycled several times. Each time the landing gear was selected down, the hydraulic pump stopped operating before the left main gear fully extended and locked and the left green landing-gear-down light failed to illuminate. When the landing gear manual extension pump handle was used, the left landing gear locked and the green gear-down light illuminated. Other than the damage to the up position and downlock switches, no other defects with the landing gear were observed that would have precluded normal operation. Based on the available information, it is likely that when the landing gear was selected down, the hydraulic pump ceased operating before the left main landing gear had fully extended and locked as a result of the broken wire in the left main landing gear downlock switch. It is also likely that, had the pilots completed the manual gear extension checklist, which included the use of a hydraulic hand pump in the cockpit, they would have succeeded in fully extending and locking the left main landing gear. There was insufficient evidence to determine why the downlock switch wires became entangled with the up position switch bracket during the accident flight.

On March 16, 2025, at 1424 mountain daylight time, a Beech C90A, N513JM, was substantially damaged when it was involved in an accident at Helena Regional Airport (HLN), Helena, Montana. The two pilots were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 other work use flight. According to the pilots, the purpose of the flight was for one pilot to undergo the flying portion of a checkride. During the flight, the landing gear was raised and lowered several times without incident. While conducting a simulated instrument approach to HLN, the pilots extended the landing gear but the nose landing gear did not indicate it was down and locked. The pilots performed a missed approach to troubleshoot the landing gear issue and were initially unable to raise the landing gear. They noticed that the landing gear relay circuit breaker had tripped (opened). The pilots reset the circuit breaker and cycled the landing gear, during which time the landing gear indicator circuit breaker tripped. The pilots reset the circuit breaker and once again cycled the landing gear. After further troubleshooting, the nose and right main landing gear indicated down-and-locked, but the left main landing gear did not. Noting the red gear in-transit lights in the gear handle were not illuminated, and the gear unsafe horn was not sounding, the pilots believed they were experiencing only a “gear indication issue” and did not complete the landing gear manual extension checklist, which included the use of a hydraulic hand pump in the cockpit. The pilots performed a low approach near the air traffic control tower at HLN and were told by the controller that the landing gear appeared to be extended. Subsequently, the pilots landed on runway 27. During the landing roll, at a speed of about 30 knots, the left main landing gear collapsed and the left wing impacted the runway surface. As a result, the airplane sustained substantial damage to the left wing and fuselage. Postaccident inspection of the airplane was performed by an inspector from the FAA and the operator’s Director of Maintenance. Visual inspection of the left main landing gear revealed several wires to the downlock switch were broken, and the Up position switch had been torn from its mount in the top of the gear well and was not located. (See figure.) Figure: Left main landing gear drag brace and switches. The airplane was lifted using jacks and the landing gear was cycled up and down several times. When the landing gear handle was selected down, the left main landing gear did not fully extend and lock and the corresponding green landing gear down light did not illuminate by the time the landing gear hydraulic pump had stopped operating. After the hydraulic pump had stopped operating, the red landing gear in-transit lights extinguished, and the landing gear warning horn did not sound. During some of the landing gear cycles, the broken switch wires would short against the airplane structure until the landing gear relay circuit breaker tripped, and the landing gear would stop mid-transit. After selecting the landing gear down, the landing gear manual extension hydraulic hand pump was used; after pumping the handle three times, the left main landing gear fully extended and locked and the green landing-gear-down light illuminated. According to technical data provided by Textron Aviation, the landing gear assemblies are extended and retracted by actuators powered by a hydraulic pump. When the actuators fully extend the landing gear, an internal mechanical lock in the nose gear actuator and a mechanical lock on each main landing gear drag brace (called downlock hooks) will hold the landing gear in the down position. In this position, the internal locking mechanism in the nose landing gear actuator and the mechanical lock on the main landing gear drag braces will actuate downlock switches to interrupt current to the hydraulic pump motor. The hydraulic pump motor will continue to run until all three landing gears are down and locked. Actuation of each downlock switch also completes the circuit to its respective green landing-gear-down light, allowing it to illuminate, and interrupts power to the red in-transit lights. The broken downlock switch wires were labeled 2-20, 5-20, 8-20, 9-20, 10-20, 11-20, and 12-20. Technical data provided by Textron Aviation indicated that, when the switch is not actuated, 2-20 completes the circuit to the landing gear unsafe horn, 5-20 completes the circuit to the red in-transit lights, and 8-20 completes the circuit to the hydraulic pump motor. Wires 9-20, 10-20, 11-20, and 12-20 are spare wires. The FAA inspector provided photographs of the landing gear of an exemplar Beech C90A located at HLN. The photos revealed that the left main landing gear downlock switch wire bundle was routed differently than the wire bundle on the accident airplane. Though figures in the airplane’s maintenance manual and illustrated parts catalog depict the routing of the wire bundle, there were no instructions specific to the installation and routing of the downlock switch wire bundles. Review of the airplane’s maintenance records indicated that the airplane operated for over 860 hours and 754 landings since maintenance was performed (in 2021) that may have required the downlock switch to be removed and re-installed. No other maintenance involving the downlock switch was recorded in that timeframe.