How could the door "lock itself"? Good question, and one that I asked
myself when it happened early on in our ownership of the 74 Cherokee
140. These "file cabinet locks" used in Pipers (and many other birds)
have quite a bit of "slop" in the cylinder and pins. So much so, that it
is entirely possible to remove the key from my door lock in ANY
position. Normally, the key should only go in and be removed when the
lock is horizontal, either locked or unlocked. With nearly 30 years of
wear (and we only have 2500 hours TT), the key can be removed from any
position.

Mike, I think that you have a good handleG on the problem. The inside latch
did not open the door in our case. I want to do some "look around" on the door
to see what can be done to prevent it again. Making sure that the key is
completely truned against the stop is one thing and, of course, I'm not sure I
turned it full open when I unlocked the plane (before the flight down, by the
way). I also want to check the baggage door since it would be an emergency
escape and does not appear to have an inside latch or unlock ability.

I had a cell phone but I still think I would have forced the door if the other
people had not been there. Kind of an unsettleing feeling when you are locked
in, it's dark and 32 deg outside.

Chuck