It seems so antiquated and weird to us today, but it wasn't that long ago that passengers could still smoke cigarettes during a flight. There were actually smoking sections on planes—which, if you’re old enough to have experienced that living hell in the sky, really didn't make things any easier for the non-smokers.

This year marks the 25th anniversary that smoking was first banned on domestic flights in the U.S. And it's been 15 years since international flights finally joined the no-smoking bandwagon.

And yet, think about the last time you visited the bathroom during a flight. You probably noticed an ashtray conveniently located on the door. What gives? If smoking is absolutely, positively not permitted during air travel at any time, for any reason, and hasn't been in this millennium, then why does every plane still come equipped with ashtrays?

Most of the experts we contacted were similarly stymied.

“I don't actually know the answer to this one,” said Ross Cheit, a Brown University professor and author of Setting Safety Standards: Regulation in the Public and Private Sectors. “My total guess would be that it is actually still a fire prevention idea.”

According to a spokesperson for the Federal Aviation Administration (who asked not to be named), ashtrays are still required because of an old FAA regulation—first drafted in 1995 and later amended in 2004—with very specific requirements for a plane's "compartment interiors" before it can be deemed airworthy. It states:

"Regardless of whether smoking is allowed in any other part of the airplane, lavatories must have self-contained, removable ashtrays located conspicuously on or near the entry side of each lavatory door.”

A rule like this probably made sense back in 1995, when passengers still occasionally needed to be reminded not to light up during a flight. But why is that rule still on the books in 2015?

"The objective for ashtrays either built into the lavatory door or designed on the interior of the lavatory near the waste chute are to have a place to extinguish smoking materials rather than throwing the burning material in waste compartments in the aircraft lavatory," the rep told us.

"Burning materials"? Such as what? Incense candles? Firecrackers? Obviously they mean cigarettes. So basically, if we can paraphrase the FAA, what they’re saying is: “You're not allowed to smoke on a plane! At all! Ever! But when you inevitably do anyway, we'll provide the ashtrays!”

Isn’t that sending a mixed message? It’d be like if the recording industry said, “It’s illegal to share pirated music online! But if you do, we’ve provided you with this handy torrent downloader.”

“One of the concerns during the fight to ban smoking was that people would still sneak a cigarette,” says Sarah Nelson, international president of the Association of Flight Attendants. “And without ashtrays, they wouldn't have a safe place to put it out.”

It’s not a hypothetical danger. In 1973, Varig Flight 820 crashed during a journey from Rio de Janeiro to Paris, all because of a cigarette thrown into a bathroom trash receptacle. It caused a fire that spread throughout the Boeing 707’s cabin, and the plane crashed, killing all 123 passengers.

Rogue smokers at 39,000 feet actually happen with some regularity. Everyone from Amy Winehouse (in 2007) to a Qatar diplomat (in 2010) have ignored no smoking signs during flights.

A 2013 flight from Canada to the Caribbean had to make an emergency landing when an entire family was caught trying to catch a nicotine buzz.

This past February, Paris Hilton's younger brother smoked various substances during a flight from London to Los Angeles, while also calling other passengers "peasants."

And last month, a Pennsylvania college sociology professor was arrested after lighting up during a flight from Nicaragua to Miami.

“Yes, people still smoke, or at least try to, even though fines have increased for tampering with the smoke detectors,” Nelson claims. She recalls personally catching “a very flustered customer” in the act. “He attempted to put it out in the trash can, and I was able to direct him to use the ashtray that was right there instead,” she says.

Those ashtrays may be a relic from a Don Draper era, but as long as there are people addicted to cigarettes who also buy plane tickets and don’t feel like rules apply to them (i.e. for as long as human beings continue to exist on this planet), those ashtrays won’t be going away anytime soon.

(Still struggling with a nicotine habit? Here are 5 Ways to Quit Smoking Today.)

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