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.

Why is this important?
If you unlock the door and, upon removing the key, twist the lock BACK
towards locking some distance, the key can still be removed AND the door
still opened. That leaves the lock cylinder somewhere in the middle.
All it takes is enough vibration to rotate the lock cylinder a little
bit towards locking and viola! The door is now magically locked. If I
recall, you SHOULD be able to get out using the inside door handle.
However, there is one lonesome sheet metal screw in the lock linkage
that can work loose. Once done the door will appear to work normally,
but there is not enough travel in the mechanism to open the door IF the
outside lock is locked. Once we tightened up all the internal linkages,
it allowed us to exit even if the cylinder is locked. 8 years later, the
problem had not returned.

We looked pretty silly on that hot July afternoon taxiing around trying
to find someone to let us out of that VERY hot airplane!!

BUT, that said, it is possible to lock yourself OUT of the plane once
things are working properly. If you don't unlock the cylinder all the
way (as I described above), leave the keys inside, and then EXIT the
bird and close the door (remember that the inside handle will let you
out), the bird is now locked with the keys inside! IF the lock is
somewhere in the middle of its travel, you can simply turn the lock with
your fingernail to complete its travel towards unlocking (you DO
remember which way that is, don't you???). However, it is entirely
possible that the lock has vibrated towards full lock, in which case,
you need the key. When this happened to me, I used a screwdriver (well,
a key actually) on the phillips-head screw for the little vent window.
Turning the screw also turned the catch until it popped open. Once done,
I could reach in and get the keys.

Try this experiment: move the cylinder until it is vertical (pointing up
and down) or some other non-horizontal position, remove the key, and
then gently bang your fist on the door in various placed mimicking
normal flight airframe vibration. You may be amazed to see the lock
cylinder actually rotate one way or the other. Depending on the
condition of your lock, it may or may not do this. It looks a little odd
when you see it for yourself.

I now make a point of turning the lock completely in either direction
before removing the key ( or checking the work of the "other person"
should she be working the lock that day).

Good Luck,
Mike

john smith wrote:
Jay Honeck wrote:

How could the door lock itself?


Wear and vibration.
Just like other things.
If you use them, they gradually lose their original shape.
Apply the right frequency and they move without direct contact.

(*Deliberately worded for multiple meanings. :-)


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