"Michael R. Grabois ... change $ to \"s\"" wrote:

On 02 Jul 2003 00:39:06 GMT, (MSu1049321) wrote:

Now wait a sec, I think I read somewhere that while gear deployment is done by
a manual switch, there IS a tie-in to the computer or to a radar altimeter such
that in the last critical seconds, a pyro will BLOW the doors open and the gear
down and locked, if the regular system fails. That could be modified, I'm
sure, some time in the next year.

And to add to what Jorge and Henry have said, there are some things you have
mixed up....

Basically, the gear deploy system works like this:

1. At 2000 ft altitude, the PLT presses the Landing Gear Arm button. The CDR
can do this too, since he's got an identical button on the left side, but he's
busy flying. When pressed, a series of relays close, some of which cause
capacitors in the pyrotechincs to charge up.

2. At 300 ft altitude, the PLT presses the Landing Gear Down button. This
closes several other relays, some of which cause a hydraulic actuator to move.
This actuator looks somewhat like a letter "C" facing downwards, and as the
"arms" of the actuator open, the landing gear is released. The gear doors and
the gear itself are mechanically linked, so that as the gear drops, the door
opens. You cannot have the case where the gear drops and the door does not
open.

3. One second after the Down button is pushed, a proximity sensor detects
whether the gear is still in place. If it is, then the sensor sends a signal to
the pyros to fire. This all takes place "behind the scenes", as only MCC can
tell if the gear is dropped hyraulically or via pyros.

The current system does have a tie-in to the GPC, however. In the Heads-Up
Display (HUD) is a reminder to the crew about the status of the gear so that
they don't have to look at the talkbacks next to the pushbuttons. At a
predetermined altitude (set by I-load), a check of the status is made, and if
the GPC thinks the gear is still up, it will flash a reminder (I think it's
"//ARM"). The gear in transit registers on the HUD as something like "//GR/",
and gear down is shown as something like "GR-DN". It's just a status on the
display, though. You can't just add a relay somewhere to make the GPC deploy
the gear, it's more complicated than that.

Do you know where I could get wiring diagrams? Being a Boeing employee,
I could probably access them online if I knew where to look.