Posted by A Squared
Over time the most frequently used holes wear. it is possible for the wear to to reach a point at which it is possible for the locking pin to pop out of the hole.
There are other factors worth noting involved in the pin pop out problem and they involve the design and placement of whole system.
The seat is prevented from coming off the rails by metal fingers that fit under the top part of the rail. There has to be some clearance to allow the seat to slide easily but in time the fingers and rail wear and the clearance grows allowing the seat to tilt back and lift the pin further than it did when new. The pin can't be made longer because the rail height and design prevents a deeper hole being drilled to receive the pin.
The third problem is that the mechanism is at the front of the seat which tries to lift when the pilot leans on the seat back as happens on rotation.
Had the system been installed at the back of the seat the problem probably would not exist because on rotation the pin would have been pushed down ...not lifted up and potentially out of the hole.
A late uncle used to say 'If my foresight was as good as my hindsight I'd be better off a darn sight'
The late model system with horizontal holes through the rail and with a horizontal pin unrestricted in length makes all the above problems go away.