Re: Squat interlock

Date:         25 Jun 99 01:32:48 
From:         "David R. Hendrickson" <>
Organization: Eskimo North (206) For-Ever
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JbTex <jbtex@aol.comkeinspam> wrote:
> I once heard pilots talking about a "squat switch" in the main
> landing gear of airliners.  They mentioned that it prevented
> the deployment of the thrust-reversers until the landing aircraft's
> weight settled onto the landing gear.  If this is true, are the
> armed spoilers also kept retracted by this switch, or must they
> deploy prior to the full "squat"?  Also, are there other systems
> controlled by squat/not-squat status? Thanks

though i've worked on '27s and '57s, the following is for newer '37s,
mostly NextGens':

737's have the squat switch in the right main gear well with a cable
running down the right leg to the scissor link.

for the TR's you can electronically fake a jacked plane being on the
ground by putting the #1 and #2 Air/Ground Override systems on the PSEU
(Prox Switch Electronic Unit, formerly EGADS; Electronic Gear and Door
System) in the Ground mode.  the plane thinks it's on the ground.

the PSEU is in the forward EE bay, forward of the nose gear.   you can
make some systems on a plane that's on it's gear think it's in the air
by using the reverse of the above.

the armed ground spoilers are kept retracted by the squat switch.  you
must remove the bolt from the cable at the scissor and pull the cable
down to deploy them (if on jacks...), the electronic trick doesn't

some systems look at the condition of the six air/ground prox switches
(2 on each gear).  others look at a combination of everything.

on the FMC in the cockpit, you can't get into the mainenance screens if
the plane's not in Ground mode.

Take Off Warning, Ram Air inlets, the NextGen's overwing hatches...lots
of systems look at the air/ground condition of the aircraft...

hope this helped...


     David R. Hendrickson
     Microsoft has announced that shipment of Windows 2000
     has been postponed to the first quarter of 1901.