B737 Flt/Gnd switch CPCS
Thread Starter
Joined: Mar 2006
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From: UK
B737 Flt/Gnd switch CPCS
Ok Guys
Just wrote this big question asking lots of interesting questions and witty observations, clicked the spell check option and lost it all....
...so short and sweet, i thought the flt/gnd switch had air logic, hence if you forgot to put it to flight before t/o it wouldn't matter, however a few days ago i was shown this not to be the case, at least in the initial climb. I've looked for some info on it, can someone shed some light???
Cheers
G
Just wrote this big question asking lots of interesting questions and witty observations, clicked the spell check option and lost it all....
...so short and sweet, i thought the flt/gnd switch had air logic, hence if you forgot to put it to flight before t/o it wouldn't matter, however a few days ago i was shown this not to be the case, at least in the initial climb. I've looked for some info on it, can someone shed some light???Cheers
G
Joined: Sep 2005
Posts: 279
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From: ???
G-Dawg: i thought the flt/gnd switch had air logic, hence if you forgot to put it to flight before t/o it wouldn't matter, however a few days ago i was shown this not to be the case, at least in the initial climb. I've looked for some info on it, can someone shed some light???
Yes it does have air logic in that if you place the flt/gnd switch to gnd while in pressurised flight then it won't depressurise. ie it is useless once airborne.
The point of the switch is to pressurise the cabin to an altitude of 200' below the departure airfied elevation before you take off. so placing the switch to flt before departure will pressurise the cabin slightly. this helps the aircraft structurally ie its a more solid object and also helps the passangers by providing a more comfortable transition to pressurised flight.
If the switch is left to gnd before departure it's not a big deal however the aircraft won't be pressurised slightly before the departure. soon as the air/gnd sensor detects flight mode then the cabin pressurises anyway and the flt/gnd switch is useless until touching down again.
the landing is pretty much the same.. the aircraft will remain slightly pressurised for the landing. if the flt/gnd switch is forgotten in GND then as soon as the aircraft touches down it'll depressurise. if it is in flt then it will remain in the slightly pressurised state until the flt/gnd switch is switched to gnd.
Yes it does have air logic in that if you place the flt/gnd switch to gnd while in pressurised flight then it won't depressurise. ie it is useless once airborne.
The point of the switch is to pressurise the cabin to an altitude of 200' below the departure airfied elevation before you take off. so placing the switch to flt before departure will pressurise the cabin slightly. this helps the aircraft structurally ie its a more solid object and also helps the passangers by providing a more comfortable transition to pressurised flight.
If the switch is left to gnd before departure it's not a big deal however the aircraft won't be pressurised slightly before the departure. soon as the air/gnd sensor detects flight mode then the cabin pressurises anyway and the flt/gnd switch is useless until touching down again.
the landing is pretty much the same.. the aircraft will remain slightly pressurised for the landing. if the flt/gnd switch is forgotten in GND then as soon as the aircraft touches down it'll depressurise. if it is in flt then it will remain in the slightly pressurised state until the flt/gnd switch is switched to gnd.
Thread Starter
Joined: Mar 2006
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From: UK
Yeah that's what i though, I have just had a running disagreement with one of the Captains here for the last week about it. Do you know at what differencial PSI the air logic will kick in as if you do leave it on grd, it will initially climb with the aircraft, up to a point then start to pressurize!
Warning Toxic!
Disgusted of Tunbridge
Disgusted of Tunbridge
Joined: Jan 2005
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From: Hampshire, UK
That diagram is interesting. I once had a faulty Right Main Gear Ground/Flight switch give a Ground signal at 33,000'. Gentle depressurisation only noticed when the TOC/Cabin alt Warning went off. I do remember seeing the cabin alt on the cusp of 14,000' before we stopped it rising.
Per Ardua ad Astraeus
Joined: Mar 2000
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From: UK
Conversely I had the air-ground switches fail in 'air mode' on landing which makes you scratch your head a bit!
As Rainboe says, we believe the activation signal is from the Rt main gear on the Classic, not the NLG.
NB: To improve the image res, rt click on the image, copy and paste into your favourite image handling prog - it might just work.
As Rainboe says, we believe the activation signal is from the Rt main gear on the Classic, not the NLG.
NB: To improve the image res, rt click on the image, copy and paste into your favourite image handling prog - it might just work.
Thread Starter
Joined: Mar 2006
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From: UK
Yes agree, IFP, thanks for posting the pics and have cut and pasted them into a doc and there great thanks, to prove to my capo all the points made above, took off with it in grd and watched as it pressurized nicely, thank you very much...thanks for all the info guys..
Joined: Sep 2005
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From: ???
g-dawg
u have much to learn about captains my friend. if you get into a discussion with them concerning the systems and they say some thing that is incorrect it is very hard for some to admit that an FO could know more than them. u know the best way to handle them is just by agreeing with them. forget reasoning. and always remember you might be right but he is always left..
on a more serious note:
BOAC: if the flt/gnd switch is stuck in flight then can't u just set the pressurisation mode selector to manual and manually open the outflow valve after landing?
u have much to learn about captains my friend. if you get into a discussion with them concerning the systems and they say some thing that is incorrect it is very hard for some to admit that an FO could know more than them. u know the best way to handle them is just by agreeing with them. forget reasoning. and always remember you might be right but he is always left..
on a more serious note:
BOAC: if the flt/gnd switch is stuck in flight then can't u just set the pressurisation mode selector to manual and manually open the outflow valve after landing?
