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  • Post last modified:September 22, 2019
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How Does Aircraft Lavatory System Works?

Do airplanes dump toilet waste in the air?

Definitely No ! Waste isn’t dropped out of the plane when you press the flush.

Lavatories on modern aircraft equipped with “Vacuum Flush” type technology to eliminate solid and liquid residue from the toilet bowl. Now no longer use of chemical toilet blue water recirculated with an electric flush in the modern airliner.

How airplane toilets are different from the home toilet?

The typical home toilet uses a bowl filled with water and a U-shape pipe is connected through it. When you flush the home toilet, it starts a siphon that drains the water from the bowl. Gravity then carries the water into the septic tank or sewer system.

The problem with this technology on an aircraft is that the motion of the aircraft. Means you cannot use a bowl filled with water. It would splash out every time when an airplane flying through turbulence. Since there is no bowl of water in the airplane toilet, you cannot use a siphon or gravity to empty the bowl.

Now the question is “Where does the toilet waste go on a plane and how does it work ?”

To answer the above question, let’s explore the inner workings of an Airplane Lavatory System for better understanding.

Water and Waste System of Aircraft A320 | ATA-38

The water and waste system supplies potable water to the lavatories and galleys of an airplane; and removes the sink and toilet waste. 

Potable water is stored in a tank capacity of 200 liters tank in an airplane.

The airplane has two drain masts. Waste water drains overboard through these two anti-iced drain masts. These wastewater comes from the aircraft galleys and from the lavatories sinks. The forward mast drains wastewater from the forward cabin and the aft drain mast drains wastewater from the aft cabin.

Differential pressure (created by the vacuum generator) discharges the waste water from the toilet bowl to waste storage tank in flight, and gravity does so on the ground. Differential pressure created by vacuum generator forces the waste from toilet bowls into the waste storage tank of aircraft.

A vacuum generator produces the necessary pressure differential while aircraft is on the ground, and at altitudes below 16000 ft.

Waste system uses clear water from the potable water system to flush the toilets.

Waste tank in the airplane has a usable capacity of 170 liters.

A water heater is installed under the washbasin in each toilet unit to supply hot water to the water tap.

The waste water is discarded outside through the drain valve (air stop valve) and the heated drain mast. Air stop valves avoid constant aircraft cabin depressurization by opening only when a certain amount of water is collected.

Toilet System Operation in Airbus A320 Aircraft

The overall toilet system operation in Airbus A320, monitoring and fault indication are controlled by the Vacuum System Controller Function (VSCF) integrated in the Cabin Intercommunication Data System (CIDS). It is connected to the Centralized Fault Display System (CFDS).

When the toilet flush switch is pressed, the Flush Control Unit (FCU) starts the flush sequence. The rinse valve and the flush valve open in sequence, controlled by the FCU, to evacuate the waste material. At the same time, the Flush Control Unit (FCU) sends a signal to the VSCF, which will operate the vacuum generator to generate differential pressure.

The vacuum generator creates the necessary differential pressure between the cabin and the waste holding tank to move the waste from the toilet bowl. Above 16,000 ft, the vacuum generator will not be started by the VSCF as the differential pressure is sufficient.

Aircraft Water Service

Water Servicing Cart is used to fill the water in the airplane. The water servicing panel in airplane contains a fitting for the attachment of a fill hose. Once the hose is attached, a fill valve is positioned to allow the water to flow into the tank. The quantity indicator on the panel is used to fill the tank. An overfill drain line is plumbed from the top of the tank to the aircraft exterior. When the water reaches the level of the overfill fitting it spills into the overfill line and is drained overboard. Often, tanks are filled until water comes out of the overflow.

Aircraft Lavatory Service

Lavatory Service Cart is used to drain the waste from aircraft waste tank. The aircraft waste tank is drained by pulling the waste drain valve handle on the toilet servicing panel after attaching the ground lavatory service cart to the 4 inch drain outlet and removing the drain plug. The tank is cleaned by attaching water pressure to the ground flush connection.

Why do your ears sometimes feel pressure changes when you flush an airplane toilet?

Flush operations of the vacuum toilet system can cause the high cabin rate of climb. This is normal for aircraft cabin pressurization. Momentarily show high cabin rate of climb indicator means pressure inside the airplane cabin changes. Your ears will feel this changed pressure when you press flush.

Why is an airplane bathroom called a lavatory?

The name lavatory comes from the Latin, meaning a room where people wash themselves.

AH Team

Our team at AviationHunt is a group of aviation experts and enthusiasts. We aim to provide the best aircraft maintenance practices, technology, and aviation safety tips.

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