First published in Flight Levels Online, Winter 2014 issue
Twin Commander Aircraft was informed recently of an event involving landing gear extension on a model 690B. The pilot reported that, prior to beginning the final approach to landing, he attempted to move the landing gear control lever to the DN (gear extended) position, but it would not move. The lever was firmly locked in the UP position. Fortunately, the incident had a good outcome — a safe, gear-down-and-locked landing.
How was that accomplished? First, a little background on the landing gear system. The landing gear control lever in Twin Commander models 690, 690A/B, and early serial number 690C/Ds and 695As is mechanically connected to the landing gear control valve located behind the landing gear panel in the cockpit. (Later model Twin Commanders have an electromechanical gear system.) The control valve directs hydraulic pressure to the gear actuating cylinders for gear extension, retraction, main gear uplock, and clamshell gear door operation.
The inability to reposition the gear selector lever likely indicates some sort of problem with the linkage connecting the lever with the valve, or so our resourceful pilot thought. He removed the upholstery on the righthand side of the control quadrant to expose the gear and flap selector valve linkages near the base of the control quadrant. He then disconnected the vertical actuator rod from the valve, effectively bypassing the gear control lever. In its place, the pilot became the gear control lever.
He reached down, lifted the arm to actuate the valve, and listened as the landing gear thunked into place in the extended position and watched with satisfaction as three green gear-safe lights glowed.
When technicians at a Twin Commander service center examined the affected aircraft, they found that the over-center cam and spring-loaded ball in the gear actuating assembly suffered from severe wear damage. The ball had worn a groove through the cam, and a substantial amount of metal debris was found in lubricant in the immediate area of the valve.
This stuck-landing-gear-lever event serves notice that pilots should be sensitive to any changes in the operation of the gear control lever. If you suspect that it takes more effort to reposition the lever, it may be an indication that the assembly is worn and in need of an inspection.
Twin Commander maintenance technicians also should be aware of the potential for wear in the gear selector assembly, and pay close attention during maintenance gear retractions and extensions and periodic inspections. If any functional abnormalities are suspected, a close visual inspection of the components is warranted. If it feels funny, look closer.
Please report any abnormal occurrences or findings involving the gear selector assembly to Twin Commander Aircraft.
