[bitwalker]

I worked on F-16 avionics (in aircraft maintenance, on the flightline), there are a lot of little nooks/holes/slots/gaps where small bits of FOD can fall and be incredibly difficult to extract, and the fear of that FOD causing a jam, flying around the cockpit, or getting wedged and causing unexpected wear on wiring harnesses and then shorting out (or worse, arcing) during flight was a _big_ deal. FOD in the cockpit was basically the worst thing that could happen during routine maintenance, because if you couldn't see it, and either couldn't get to it with a magnet (or the FOD wasn't metal), it might require pulling _a lot_ of stuff out of the cockpit before you could reach into the area where it fell. The worst case that could easily happen was having to have Egress come out and pull the ejection seat so you could get under it.

I always figured that all of those little gaps/etc. were due to a couple factors:

1.) the aircraft are constantly being upgraded/modified, so even if you designed the aircraft to be gap-free initially, there will inevitably be changes that introduce them. The cockpit itself is basically a frame with racks that hold all of the avionics, seat, etc.

2.) in conjunction with the above, ease of maintenance was somewhat important, so they tried to leave at least a little room to maneuver in the cockpit where possible (though there were plenty of places which were a nightmare to work regardless), but that comes at the cost of introducing areas where things can fall.

3.) some components have to be regularly removed and worked on outside the aircraft, or must be free of obstruction during flight, e.g. the ejection seat. So you end up with plenty of gaps where things can fall.