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AACs - Part 1-40 - Airworthiness Articles
Part 1 - Airworthiness Articles
Landing Gear Switch Inadvertent Operation
Note: The following article has been reproduced in entirety from BASI Journal No 7, Autumn 1990.
The pilot of a six place, single engine, retractable gear aircraft was extremely embarrassed when the landing gear retracted during touchdown and the aircraft slid to rest on the runway.
The gear retracted because the selector had been accidentally bumped to the UP position by the front seat passenger's left knee.
But how could this be so? The selector is supposed to have a lock at the UP and DOWN positions requiring the operator to physically pull the knob out of the lock before a selection can be made. On this occasion the passenger's knee movement was all that was required.
Inspection of the switch revealed that its plastic knob had been screwed onto the switch arm too far. This action withdraws the lock tangs and renders the switch inoperative.
The plastic knob is normally locked in its vertical position by a small steel grub screw. This had become loose for reasons unknown, (age and UV light do have a detrimental effect on plastics), and the normal action of a pilot would be to simply screw the knob further onto the shaft until it became tight again, unfortunately with embarrassing results.
Many general aviation aircraft with retractable landing gear have this common switch mechanism. The problem is not an isolated case, so don't become another victim of this "Murphy".