How Do Airplane Toilets Work? All You Need to Know About Aircraft Water and Waste Systems.
Why do we have Airplane Toilets? A toilet in a vehicle that moves in the air? Yes, that’s certainly a mystery that’s worth exploring! Where does the waste go? How does the water get into the toilet? Why the loud swoosh sound when you flush airplane toilets? Many people have pondered on these questions, and for good reason, especially considering all the very myths that go around. This article will provide all the information you need to know, not just about airplane toilets, but also comprehensive information about aircraft water and waste systems.
The following will be addressed in this article:
- Normal Toilets vs Airplane Toilets
- The History and Future of Airplane Toilets
- Aircraft Water Systems:
- Aircraft Potable Water Systems
- Aircraft Waste water systems.
Normal Toilets Vs. Airplane Toilets
First, here’s a shocker. Airplane toilets actually use a vacuum system rather than the typical water system used in your regular toilets – the ones on the ground. This vacuum system sucks waste out of the toilet bowl and keeps it in a special tank that is usually located in the back of the plane. When the toilet is flushed, fresh water enters it through a control valve. The wastewater then flows through a series of pipes, into the waste tank. The vacuum is created by a pressure difference between the cabin and the waste tank; while the cabin is pressurized, the waste tank is not. The toilet bowl is usually made of PTFE, a non-stick material.
Once the plane lands, the collected waste is moved via specialized tankers and then discharged into a designated drainage system. The waste is then mixed in with the waste at the airport’s or other facility’s toilet. The airplane tanks are always cleaned and disinfected with another hose after the waste is removed from them.
The aircraft’s water servicing panel has a waste drain valve assembly and a waste tank rinse fitting assembly. The waste is first drained out of the plane tank by connecting it to a large drain hose which is in turn connected to a waste collector. The hose uses suction pressure to drain out the waste. The empty waste tank is then cleaned out using a cleaning solution – a mixture of cleaning products and water. This solution is injected from the waste tank rinse fitting assembly into a cleaning nozzle which rinses out the waste tank.
Normal toilets, on the other hand, use water and gravity to operate. When you flush, water siphons the waste and gravity pulls it into a sewer system or septic tank. This is not feasible on an aircraft as there is no onboard septic tank or sewer system. Water cannot be placed in the toilets because each time the plane moves, the water would splash about. The only water supplied to the toilet is a little amount, enough for cleaning the toilet bowl and readying it for the next person. There is a blue cleaning liquid called Skykem– the main ingredient in blue ice –added to the water. Skykemdisinfects the toilet bowl and kills foul odors in the toilet.
The loud swoosh sound made when you flush airplane toilets is owing to the vacuum mechanism. Also noteworthy is that the speed at which the content is sucked out of the toilet is super high.
The structure of airplane toilets means that:
- They can be placed anywhere on the plane.
- They can flush in several different directions.
- They use pipes that have very small diameters and can thus be placed anywhere in the airframe.
- The pipes do not necessarily have to face downwards, since the toilet mechanism is not dependent on gravity.
- Since there is only a small amount of water used, they are lightweight and can be easily installed. The lightweight quality is especially appreciated in aviation where weight savings are of utmost importance.
The History and Future of Airplane Toilets
The modern airplane toilet was invented by James Kemper in 1975 but was not installed in Boeing planes till the 80s. Before then, passengers relieved themselves in a slosh bucket or bottle, which did not flush and was kept in the plane until it landed. One major problem with that toilet was spillage.
In 2016, a new airplane toilet prototype was developed by the aircraft manufacturer, Boeing. The prototype features a larger toilet bowl and a self-cleaning mechanism after each use. UV light is released into the lavatory for 3 seconds, a duration that is enough for 99.99% of the pathogens to be eliminated. The UV lights are strategically placed so they can hit important spots around the restroom, including the countertops, toilet seat, and sink. The lights also get rid of the bad odors.
Boeing is also working on hands-free restroom options. These will allow passengers to use the tap and soap, place things in the trash and lock the door without making contact. The result of this would be a friendlier, easier, and cleaner toilet experience. There are also some plans to introduce quieter vacuum pumps.
Aircraft Water Systems
Aircraft have two distinct water systems: potable water systems and wastewater systems. For sanitary reasons, it is imperative that these two systems work separately.
Aircraft Potable Water Systems
Drinkable (potable) water is supplied to the aircraft via a water truck, AKA a water servicing cart, that is used for aircraft ground service. Some airport terminals offer a water cabinet, which is a direct hose connection to the airport water supply.
The water trucks usually have a low profile, enabling them to fit below the aircraft wings. The trucks connect their water supply to check valves by means of couplings. Once the hoses are fully secured, the check valves are opened to allow water to flow from the truck. Water is then pumped from the trucks to the potable water tanks situated within the aircraft fuselage. An overflow valve is used to prevent an overflow of water past a set level, depending on the aircraft. In Boeing 737s, the number is 30 gallons (0.13 m3). The overflow valve has a drain line that is plumbed from the top of the tank to outside the aircraft. Once the water reaches that set level, it spills into the overflow line and is drained overboard.
Just enough water for the flight is filled in the aircraft before take-off. Some airlines avoid filling the water tanks completely in order to save weight, and therefore fuel efficiency.
Within the potable water tank, there are sensors that give the flight and cabin crew an indication of the amount of potable water left in the tank. An electric pump pressurizes the potable water to ensure there is a positive flow rate towards the galley, the washbasin, and the toilet. Pipes are carefully laid out between the tank and galley and lavatory to ensure the water is distributed appropriately. Heat trace wiring fitted to the pipes ensure that the plumbing lines do not freeze at the low temperatures present at high flight altitudes.
Some long-haul aircraft with flights lasting 20 hours or more have showers on board for luxury travelers. In this case, water is also supplied to the showers. The water is delivered at warm temperatures by means of a fitted water heater and the showers are timed to conserve water; water conservation also translates to weight savings.
The water pressurization system comprises a pressure regulator filter, a pressure relief valve, and an air compressor. These work together to ensure the water is kept at cabin pressure. The air inlet (compressor) is linked to the plane’s pneumatic system.
Cabin maintenance mechanics see to all the disinfections and water sampling. The water tanks, lines, and plumbing fixtures must all be disinfected after use, or before refill. At every airport where a refill occurs, there must be a way to determine the quality of the water. This involves getting a report from a certified lab that shows if there is coliform bacteria in the water, an indicator that the water may have been contaminated by microorganisms. E. coli bacteria is particularly harmful to humans when consumed.
Even though the water is said to be potable, it is not advisable to drink this water as there are various possible points of contamination along the water system. For this reason, bottled water is served aboard aircraft. The water used for cooking or preparing beverages comes from the potable water supply but is usually distilled or filtered to make it suitable for use.
Testing of aircraft water conducted by Health Canada in June 2005 showed that 15.1% of the water tested positive for total coliform bacteria, while 1.2% tested positive for E. coli. These numbers are not a risk worth taking, as even trace amounts of such bacteria can cause poisoning.
Aircraft Wastewater Systems
Greywater – separate from toilet wastewater – is usually ejected from the aircraft mid-air via a drain mast, an external vertical winglet that is heated to prevent the water from freezing. The ejected water usually evaporates once it enters the atmosphere. If the sinks or basins are used while the aircraft is on the ground, the water lands on the runway.
The drain mast makes use of an air stop valve to allow the one-way flow of fluid out of the drainage system. Otherwise, air flowing into the plane could depressurize the cabin. Flow through the air stop valve is controlled by a paddle and two seals. A negative pressure differential keeps the valve closed until the weight of the water column overcomes the negative differential. The valve also prevents large backflows of water which could result in pipe clogs.
Conclusion:
So, there you have it. The toilet waste is safely kept away in a tank until the plane lands. Waste is definitely not released into the air. However, there have been some credible reports in the past of “blue ice” landing on people’s homes. This supposed blue ice is a mixture of waste and Skykem. The mixture freezes when the plane is at high altitudes, and then leaks out of the plane’s undercarriage as the plane gets closer to the ground during landing and the temperature gets warmer. Nonetheless, this is a very rare occurrence. The UK only reported 7 cases in 2017, out of 2.5 million flights that occurred in the UK airspace that year.
Aircraft toilets and waste systems are definitely different, but not complex.
References
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