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philbrown

Seatbelt Auto Logic

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Whats the logic with regard to having the seatbelt sign selected to auto. Does the aircraft automatically turn the seatbeltsw on and off, and if so, at what sort of levels.Thanks for any help.-Phil

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If it's anything like a 757/767, with the switch in AUTO the seatbelt signs will be illuminated whenever the flaps are extended or the aircraft is on the ground.So the lights go off on selection of Flaps Up and come back on when the first stage of flap is selected for the approach.Don't know of any airline which uses the function though!Andy.

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Just a completely unuseful and unused function.

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Thats not exactly true, The Seatbelt sign and no smoking signs auto function means that the sign will turn on or off when passing 10.000 FT.

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The logic may vary from airline to airline. Some airlines rewire logic so that the No Smoking Signs are on all of the time (whenever the aircraft has electrical power... even though the knob still has 3 positions).On our NG's (and no doubt a few other airlines), the AUTO logic puts the Fasten Seat Belt signs and No Smoking signs ON when:Landing gear is down or when the emergency oxygen masks are deployed.Trailing edge flaps are not up.There may be some NG airlines with an airplane altitude triggered switch, but I can't confirm this. On our 767's and 747-400's, the cabin altitude being at 10,000' will trigger the signs... which is slightly different from airplane altitude ;-) Our NG's and other airline's NG's I've come across, use a Cabin Altitude trigger of 14,000 feet! (I don't know why there should be such a big difference)."Thats not exactly true, The Seatbelt sign and no smoking signs auto function means that the sign will turn on or off when passing 10.000 FT."One thing you learn pretty quickly when you work on dozens of different airlines is that nothing is exactly true... or exactly false ;-)Cheers.Ian.

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It can also be used to trigger the "beep" you always hear informing the Flight Attendants of altitude, status, etc. Just switch it to auto and switch it back.Nick B.Continental Airlines 737NG Pilothttp://www.precisionmanuals.com/images/forum/800driver.jpg--AMD Athlon XP 3200+ @ 2.2 Ghz (Equal to 2.8 ghz)400W Power supply3x 80 mm Case FansSoyo VIA KT600 Dragon PlusnVidia GeForce FX 5200 128 mb2 x 512 PC400100 GB Western DigitalMicrosoft Sidewinder Precision 2

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"cabin altitude being at 10,000' will trigger the signs... which is slightly different from airplane altitude"Are you sure about this? Im'm not certain that cabin altitude ever exceeds 7,000 by much! If it did, as cabin crew, I could expect to be a busy person with the oxygen bottles!

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>"cabin altitude being at 10,000' will trigger the signs...>which is slightly different from airplane altitude">>Are you sure about this? Im'm not certain that cabin altitude>ever exceeds 7,000 by much! If it did, as cabin crew, I could>expect to be a busy person with the oxygen bottles!Thats exactly the point. If the cabin altitude is that high you need the pax in the seats, hence the need for the signs to be on ;)

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As Fred says, the airplane logic takes into account cabin pressurization problems (including rapid decompression). The oxy masks will deploy automatically... so you want everyone sitting down... and certainly not smoking :-)On some aircraft, the Return To Seat sign in the toilets will be inhibited (if you are in the toilet and foolishly decide to walk back to your seat to put on your oxy mask, you may not make it back.The emergency decompression announcement is also tied in with parts of this system.Hope this makes sense? If not, ask your friendly company avionics engineer.Cheers.Ian.

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Well, when I see it written down, everything becomes blindingly obvious - Thanks both! Now older and wiser..

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