Bonjour,I would like to know what is the difference between AUTO and ON for the Seat belt/No smoking sign on the overhead panel.Is there a specific logic applied when the switch is set to AUTO.MerciBest regards.Claude

Caude,I believe the auto, as it sounds, goes off at a predetermined time, while "on" will make it go off right away, regardless of the conditions.In any case I believe that in PIC it does not matter, i.e. in auto, the chimes do not sound at any particular time.Regards,WS(Kewr)

When the No Smoking sign is in auto, the no smoking light is extinguished when the gear is up, and are lit when the gear handle selector is placed "down." The Seat Belt signs, when in auto, are extinguished when the airplane climbs through ~10,000 ft, and are lit again as the aircraft descends through ~10,000 ft.When in Auto, both signs will automatically come on if the cabin altitude exceeds about 10,000 feet, such as in the case of decompression.Jon (KSEA)

Our aircraft have the AUTO seatbelt sign selection connected to the flap lever. When the flaps are out of up the seat belt sign is on.

Our seatbelt is linked to the flaps too.And wouldn't the signs come on regardless of switch position in a decompression?

>And wouldn't the signs come on regardless of switch position >in a decompression? They certainly would :-) (It took me a while to get an answer to this one, didn't it :-)).Just looking at the wiring diagrams now (whose, I can't recall)..... A "greater than 10,000' cabin altititude" pressure switch activates two relays, putting on the FSB and NS signs...and sending a signal to the Passenger Address Amplifier to sound the FSB/NS chime throughout the cabin (I wasn't sure if the automatic Emergency Decompression announcement would override the chime, but there seems to be a mixing circuit rather than a priority circuit in the PA amplifier which handles these two). The PA amplifier, by the way, is bristling with priority circuits... with the Captain's mic having the highest priority (lowest priority is Boarding Music).Selecting the FSB and NS to "On", manually, activates these same two relays... as does selecting "Auto" and satisfying the On logic.The FSEU (Flap/Slat Electronics Unit) and the PSEU (Proximity Switch Electronics Unit) provide the signals to activate the FSB and NS signs. The FSEU provides "Flap Lever not in retract" logic. The PSEU provides "Any gear not up or any gear door not closed" logic c/o proximity sensors on the gear and gear doors (rather than just a simple Gear Lever position switch). Today's useless piece of information ;-)Cheers.Ian.

Not useless at all Ian!The interesting choice by Mr. Boeing to have the No Smoking signs 'connected' to the gear causes some confusion with Cabin Crew. Although we have a strict no smoking at all times policy we often switch the NS sign to auto for night flights to darken the cabin. On approach the FSB sign illuminates when flaps 1 is selected and the cabin crew all sit down, however a short time later another chime is heard as the gear is lowered (the NS sign coming on). It has been interpretted as the FSB sign going off again! Pays to look at the little lights!

"On approach the FSB sign illuminates when flaps 1 is selected and the cabin crew all sit down, however a short time later another chime is heard as the gear is lowered (the NS sign coming on). It has been interpretted as the FSB sign going off again! Pays to look at the little lights!"Interesting. I can't think of any way to prevent this (at least not on night flights)... other than training the cabin crew to look out of the window to see how close to the ground they are :-lolOn a related subject, there was a recent message thread on the PPRuNe site (I think) which talks of one of the requirements for a certain approach into Narita (Tokyo)... The gear must be lowered before crossing the coastline... to prevent iceblocks dropping on villagers/townspeople under the flightpath! I knew about leaky toilet valves creating large blue iceblocks, but I didn't realize that substantial quantities of ice also formed on the gear/gear doors.Cheers.Ian.