It is possible to close the Europa doors leaving the aft shoot bolt out the
hole, (due to the asymmetric force from the gas strut , and a front handle
?). In early flights the doors are frequently closed by helpers from the
outside but from the inside the result is less easy to detect. There have
now been at least two incidents resulting in loss of a door in flight. So if
you are of the IICHIWH school read on.
The simplest warning system would have switches in series detecting the
presence of all four bolts in the holes, either by fitting metallic rings in
the holes or, if you have fitted 35mm film cans over them to keep the water
out, then push switches mounted in the ends. This system has the
disadvantage that you cannot work with doors open and the electrics on
without the warning going. An override has an obvious disadvantage, so you
could fit extra "door in the frame" switches to activate the system ; but
the following is simpler and based on the fact that you don't really need
the front pair for alarms (you would need your eyes permanently shut not to
detect the front closure, and you would hardly get to taxying before the
door flapped anywa) so :-
Fit NC's to the rear and NO's to the front ( you know what these are
following the recent lectures (:-))) Wire all four in series to activate
the alarm. You can then work happily away with either or both doors open
without wearing ear plugs ( IMHO such an important alarm needs to include a
cabin siren , the u/c one if fitted) and it all comes live when both doors
are (nominally) closed.
As a bonus, if the front switches are arranged to close before the back ones
open, then you have a free self -test, as there will be a brief beep when you
throw the handle.
The perceptive will notice that while you can happily taxy with one (or
both) door(s) open, the alarm fails if a door leaves the aircraft .... but
if you have ignored it that long, you don't need a siren, rather two SOS's
(the second being a Solenoid Operated Spike).
Graham (& Ted)
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