Ever wondered how do aircraft lavatories work? They have come a long way since the concept of flying loos was incorporated for military as well as commercial use.
How did it Start?
It started when the on-board personnel would excrete into bags and loft it overboard! That’s it! But imagine a kilo lump of fecal matter falling from a height of 10,000 ft directly onto someone or something below? No need to imagine, coz it is a reality. That’s right, feces thrown overboard from early aircrafts have hurt people and damaged property in the past. Seeing the repercussions of such events, it was soon forbidden to throw excrement overboard and the need to build loos within the aircraft became necessary.
How did the Toilets evolve?
So it started out as mere buckets with chemicals placed in them. These chemicals would interact with the feces to decimate the stench and deodorize the aircraft. These toilets were called ‘Chemical toilets’ and were most often kept in larger aircrafts towards the back. For example the British bomber aircraft Avro Lancaster used this during World War II sorties. Soon, they became standard fitment in long-range commercial aircrafts and were given separate cabins where the buckets would be kept over chair with holes at the appropriate place.
Then next-gen toilet evolved in the form of Siphon toilets. Electric pumps would circulate blue liquid to facilitate siphoning off the feces from the bowl all the way into storage tanks below. Each flush would need to be refilled with this blue flushing fluid and the storage would be done under depressurized tanks. The downside was soon recognized as the adding many gallons of such liquid would make an aircraft heavier, increase the fuel consumption and decreased passenger capacity. To exacerbate this cause, the depressurized tanks would often leak and thaw out as the aircraft descended and would often fall as ‘shit-hail’ onto people and property below. As per records, 27 instances have been reported between 1979 and 2003 of such shitballs falling from the sky and damaging things on the ground.
What kind of lavatories are used today?
In 1975, Mr. James Kemper patented the Suction toilet that are in use today. The patent information can be found on this link. Although the patent was made in 1975, they didn’t come into service until 10 years later. These toilets have powerful suction and Teflon-slick walls that take down all fecal waste frictionlessly downwards into the sewage tanks using just a bit of water.
You must have noticed that there isn’t really a lot of water flow during the suction. They perhaps use lesser than 300 ml of water per flush. This made the toilet very economic as compared to the Siphon toilets that were in use earlier. When the flush button is pressed, it opens a valve which exposes the waste to a pneumatic vacuum which sends the load through the aircraft’s sewer lines into a 650 liter holding tank. This tank is thankfully pressurized like the rest of the aircraft and hence poses no risks of leaks and formation of ‘shit-balls and shit-hails’.
Upon landing, janitors have to suck out the waste of the sewage tank and dispose it into a sewage treatment plant available on most airports.