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The lavatory is one of the make or break elements for aircraft passengers that can affect their entire travel experience

According to Claudius Wahl, Vice President of Marketing and Business Development BFE/Retrofit at Diehl Aerosystems, there is a growing demand for hands-free aircraft toilet functions. These include touchless flush, seat/lid, taps, soap dispenser, waste bin and even the door. Asia and the Middle East are leading the trend, for cultural reasons, but North America is moving in the same direction.


Analysis has revealed two types of perception: subjective and objective. Subjectively, and so more difficult to quantify, passengers have four main areas of concern in aircraft lavatories. In order of importance, they are smell, lighting, colour and shape. Objective perception describes visible dirt and stains.


Noxious odours are caused by microbes and spillages and anti-microbial coatings are an increasingly popular solution to this. The use of larger one-piece components, for example combining a toilet surround and splash panel or fitting a one-piece floor unit, avoids seams, which can become dirt traps. They are easier to clean and make the space appear larger, while a one-piece floor unit also has the advantage of preventing seepage from damaging the aircraft structure underneath. This is not to be taken lightly – a fatal accident in 1971 was caused by the catastrophic failure of a corroded rear pressure bulkhead and subsequent explosive decompression.


While the flexibility of large composite components gives designers greater potential to produce moulded shapes that make an attractive space, the choice of materials is limited as they have to meet very strict fire, smoke and toxicity standards. Paint is not an option for the same reason but digital printing and water slip transfers are opening up new opportunities. This can now be supplemented by LED mood lighting, using colours that give a clean and fresh appearance.


Not directly related to hygiene, but still a consideration in lavatory design, is the fact that many aircraft galleys do not provide for liquid disposal. As they are usually located next to a lavatory, the washbasin is often used by cabin crew to dispose of unwanted tea and coffee, causing discolouration. This situation is unlikely to change in the short term, so new stain resistant coatings are under investigation.


As cabins become quieter, other system noises are revealed for the first time. One of the most prominent is the lavatory flush, along with the constant air extraction. Wahl says the flush has become quieter over the years, adding that water efficiency is pretty good and there is little more improvement to be made as careful shaping of the bowl can generate a swirl pattern that gives maximum coverage for the lowest volume per flush. 


The noisiest toilets are those with a vacuum extraction system, the suction force being so great that the piping is usually made of titanium. The development of stronger carbon fibre reinforced plastic now provides a much cheaper but equally resilient alternative. It is also being introduced into galley waste-disposal systems.


Diehl has adapted the ventilation grille in the door to reduce some of the extraction noise leaking into the cabin but, for the extraction system itself, the air has to pass through a smoke detector and a particle filter before it enters the aircraft’s environmental control system (ECS). This requires a much higher flow rate to overcome the pressure drop caused by the filter. 


Wahl says the company is now looking at ways to introduce a bypass system so that the air is still monitored for smoke but the overall flow rate is reduced and so is quieter. This could be improved further with introduction of Diehl’s foam tubing currently used elsewhere in the ECS. The foam has many tiny holes that allows air to pass through without the usual hissing sounds. >>

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