Roy Smith wrote:
Denny wrote:

Regardless of the motion of the door in opening, you can count in there
being pressure sensors that block the locking mechanism from actuating
when the pressure in the cabin is higher than external pressure...
They don't all have to be electrical to still be safe in case of total
electrical failure... A simple bellows mechanism, no different from
your altimeter, can push a locking pin into the doors hardware anytime
the inside pressure exceeds the external pressure...


There must be some kind of override to this. Imagine the situation of
a plane sitting on the ground with a fire in the cabin. I would
imagine that would make the inside pressure higher than the outside
pressure, but clearly not a case where you want to prevent the doors
from opening.

I know that our airline evac checklist includes the pushing of the
emergency depress. Otherwise the main door will not open. Had to test it
a few times and it is kinda fun....
The more I thought about it a simple differential pressure switch that
dis-engages the handle would work nicely.

Michelle