I've wondered why airliners have a switch in the cockpit to turn off the non-smoking sign. Why isn't it illuminated all the time, or a better question: Why is it still there, now that everybody should know.
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$\begingroup$ A few airlines still allow smoking on some flights (none in the US though). $\endgroup$– Michael HamptonCommented Jul 22, 2016 at 22:41
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2$\begingroup$ to me this is not a duplicate: this question asks why, the other asks if. $\endgroup$– FedericoCommented Jul 24, 2016 at 12:05
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1$\begingroup$ I think this is a duplicate as there is information in the answers of the question linked that may answer this question $\endgroup$– Manu HCommented Jul 24, 2016 at 19:03
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2$\begingroup$ @DavidRicherby but is a secondary answer buried down beneath the accepted one. it is not given, even if this gets closed as duplicate, that would be easily found by a visitor. $\endgroup$– FedericoCommented Jul 25, 2016 at 10:30
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1$\begingroup$ @Federico Really, I don't think it's at all hard to find in the answers to the other question. I'd expect anybody who was curious about this question to at least skim all the answers anyway: that's what people who are interested in something do. $\endgroup$– David RicherbyCommented Jul 25, 2016 at 10:37
2 Answers
Smoking was outright banned on flights in the US in 1998/2000 which was in reality not all that long ago. It should be noted that smoking on domestic flights under 2 hours was banned in 1988 and under 6 hours in 1990. With that in mind we must remember that there are plenty of planes that are still in service and older than that, many were designed long before that time as well. In the view of the airlines its simply cheaper to leave the lights and switches there than put in a new interior panel in many cases.
Also as mentioned in the comments planes are built for the global aircraft market and there are still countries that allow smoking on flights. This question is similar and has some good info as well.
But here in the US the main reason is because the FAA mandates the signs,
For charter (135) operations
§ 135.127 Passenger information requirements and smoking prohibitions.
(a) No person may conduct a scheduled flight on which smoking is prohibited by part 252 of this title unless the “No Smoking” passenger information signs are lighted during the entire flight, or one or more “No Smoking” placards meeting the requirements of § 25.1541 of this chapter are posted during the entire flight. If both the lighted signs and the placards are used, the signs must remain lighted during the entire flight segment.
For scheduled commercial (121) operations
...
(c) No person may operate an airplane on a flight on which smoking is prohibited by part 252 of this title unless either the “No Smoking” passenger information signs are lighted during the entire flight, or one or more “No Smoking” placards meeting the requirements of § 25.1541 of this chapter are posted during the entire flight segment. If both the lighted signs and the placards are used, the signs must remain lighted during the entire flight segment.
The reason they are not lighted the entire time most likely stems from history. Since there is a switch to turn them on chances are there is a check list item to flip the switch. You will most likely see them go on and off when the pilot hits that item on the pre flight checklist that may occur at the gate or on the taxiway heading out for take off.
The Piper Archer I fly still has ash trays (there is even one in the pilots seat arm rest)...
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13$\begingroup$ Also, it needs a switch simply because you don't want to have things come up on their own immediately when the electric bus is powered. It is a good general practice with electricity to power the line with appliances detached and then connect them one by one that doubly so applies to aircraft systems. $\endgroup$ Commented Jul 25, 2016 at 19:07
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2$\begingroup$ Your link to countries that still allow smoking is 14 years old. I highly doubt it's still accurate. $\endgroup$ Commented Mar 18, 2017 at 18:35
Dave's answer is largely correct, but it's probably also worth mentioning that many newer airliners have no such switch... because they have no lighted "No Smoking" signs at all. Instead, they use permanent placards.
While the regulations that Dave cited do require the No Smoking signs to be lit for the entire flight if they are present, it also allows permanent placards to be used in lieu of the lighted signs:
(c) No person may operate an airplane on a flight on which smoking is prohibited by part 252 of this title unless either the “No Smoking” passenger information signs are lighted during the entire flight, or one or more “No Smoking” placards meeting the requirements of § 25.1541 of this chapter are posted during the entire flight segment. If both the lighted signs and the placards are used, the signs must remain lighted during the entire flight segment.
For example, this picture is from the passenger cabin of one of Delta's new 737-900ERs with the Boeing Sky Interior:
Delta Boeing 737-900ER No Smoking Placard
Note that the seat belt sign is still lighted and switched from the flight deck, but the No Smoking sign is just a permanent painted placard.