What Is a Lavatory?
QUICK ANSWER
A lavatory is the bathroom on an airplane. It is a compact restroom with a toilet and sink that uses a vacuum flush system instead of water to pull waste into a sealed tank. Planes have one or more lavatories depending on size, and smoking in them is illegal.
Lavatory is the word airlines use for the airplane bathroom, and while it is a familiar little room, how it works is more clever than most passengers realize. Here is what a lavatory is, how the distinctive vacuum toilet functions, how many you will find on a plane, and the firm rule against smoking in one.
What is a lavatory?
A lavatory is the term for a bathroom on an airplane. It is a small, self-contained restroom, usually just big enough for one person, containing a toilet, a compact sink with running water, a mirror, and a waste bin, along with soap and paper towels or a hand dryer. The name is a more formal word for a washroom, and airlines and crew use it consistently, so you will hear flight attendants refer to the lavatory or lav rather than the bathroom. A lighted sign in the cabin shows whether a lavatory is occupied or vacant. Everything in a lavatory is designed to be compact, easy to clean, and able to function safely at altitude.
How does an airplane lavatory work?
The most distinctive feature is the toilet, which uses a vacuum system rather than a tank of water like a home toilet. When you press the flush button, a valve opens to the aircraft's waste system, and the pressure difference creates a strong suction that pulls the contents down and back into a sealed holding tank at the rear of the plane, using only a small amount of a slick liquid to rinse the bowl. That is why the flush is so loud and forceful. Using vacuum instead of gallons of water saves enormous weight and works reliably at altitude. The holding tanks are emptied and serviced by ground crews after the flight, not released in the air.
How many lavatories are on a plane?
It depends on the size of the aircraft and its seating. A small regional jet may have just one lavatory, while a single-aisle plane like a Boeing 737 or Airbus A320 typically has two or three, usually one at the front and one or two at the rear. Large wide-body aircraft used on long-haul flights can have anywhere from a handful to a dozen or more lavatories spread across the cabins and sometimes on a lower deck. Airlines balance the number against seating, since every lavatory takes space that could hold seats. Premium cabins often have their own dedicated lavatories, which is one of the quieter perks of flying up front.
Can you smoke in an airplane lavatory?
No, and it is taken very seriously. Smoking is banned on all commercial flights, and that absolutely includes the lavatory, which is why every airplane lavatory is fitted with a smoke detector. Tampering with or disabling that smoke detector is a federal offense that can bring heavy fines and even arrest on landing. The signs and safety briefings specifically warn against it because a fire in the confined space of a lavatory would be extremely dangerous in flight. This applies to vaping and e-cigarettes as well as traditional cigarettes. If you use tobacco, you will need to wait until you have landed and left the airport's secure area, since the no-smoking rule is strictly enforced everywhere on the aircraft.
A lavatory is the airplane bathroom, a compact restroom whose toilet uses a powerful vacuum system to pull waste into a sealed tank rather than flushing with water. Planes carry anywhere from one lavatory to a dozen depending on size. Smoking or vaping in one is illegal, and every lavatory has a smoke detector.
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