Thanks to all for the input on the alt air door.  Never doubted the need for
the door, just how to be sure the manual override is foolproof and foul
proof.  I think the idea of having a micro switch installed with an
annunciator to tell you it's open - then add a checklist item before takeoff
may be the best answer.  The system I have incorporates a stiff cable snaked
across the cowl through a cable housing and then the last four inches or so
at the door has a flexible cable with swaged loops on the ends - the
flexible cable allows the door to automatically operate.  Worries raised are
that the stiff cable could freeze inside the sleeve from dirt over time and
disuse, or the flexible cable could somehow get hung up on the loops when
there is slack, not allowing the door to close again.

I appreciate the advice and sharing of experiences.

Best,
John Barrett