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On 10/03/2014 10:22 AM, Brian Davies wrote:
> Am I missing something here? If you have a door warning circuit
> that brings a red light on when the door is open why do you need a
> test circuit?
Whether you have a red light that comes on when the door is unlocked,
or a green light that goes out when the door is unlocked, both systems
can fail easily.
A lit green light might be caused by the switch sticked in the on
position, or a red light might not lit because a wire is broken.
If we would rely on lights instead of a physical confirmation that the
door is locked, we would for sure have more door-incidents!
A solution is to have a test-switch, so you can confirm that the
system is working properly.
This means you have to put "test the door lights" on your checklist.
Another solution is to monitor the change of state of the lights while
closing the doors. A red light should be lit and then go out while
closing the doors, or a green light should be off and then come on
while closing the doors. This means you need to be aware of what you
are doing while closing the doors and monitor the light.
Bottom line is:
Instead of feeling that the door is closed we now have to push a
button, or we have to monitor the change of state of a light.
We don't gain anything by this.
I'm fond of gadgets in my airplane, but this one didn't make it for
the reasons above. It is completely useless. One potential for missing
something on the checklist is then replaced by another potential to
mis something on the checklist.
Frans
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