There have been many developments in waste/water system technology on-board commercial aircraft in recent times. Most of these developments are linked to the increased complexity of the systems with respect to the communication between the equipment and system status indication.

Technological developments

Torsten Böttger, vice president of engineering at Diehl Aviation and Dr Gerd Wedler, head of system engineering at Diehl Aviation, points out that new potable water circulation systems control both the water pressure and water flow by means of a new kind of potable water pump.

“This system leads to no pressure loss, even for parallel use of various supplies, and symbolises positive progress in water system technology,” they say.

“Additionally, the development of disinfection applications for potable water systems is increasing in order to manage sterilisation during water circulation, without the collateral effect of neutralised bacteria. For example, the water treatment module for the Airbus A350 for high potable water quality manages the sterilisation continuously during the water circulation upon filling.”

“On the Airbus A350, a potable water treatment module has been introduced that uses ultraviolet (UV) radiation to decrease the risk of microbiological contamination of the system,” says Jürgen Winkler, aircraft system engineer at Lufthansa Technik.

“We expect less maintenance effort to disinfect the potable water system, thanks to extended interval. The benefit of the potable water treatment module is currently being validated.”

One of the most important improvements from Boeing with regard to waste/water/systems (WWS) is also the installation of a UV water treatment module.

“This module is part of the Boeing 787 design. The ultraviolet water treatment module cleans the ground service water of any remaining disease organism during the potable water filling operation,” says Yannick Canagassabe, cabin engineer & minor repair CVE at Air France Industries KLM Engineering & Maintenance (AFI KLM E&M).

“WWS has been fairly stable, with key step changes over the last few decades reducing weight, introducing redundancies and improving the overall reliability of the systems,” says Lamia Khaled, director, sales and marketing for Lavatories and Water/Waste Systems at Rockwell Collins.

“In recent years, with the drive for a more connected aircraft, there has been a trend in introducing additional maintenance diagnostic and communication capabilities. This enables airlines to better track the WWS performance and have a better forecast around spares requirements, consequently reducing delays.”

A significant amount of research and development is currently on fibre-plastic reinforced applications to save weight and costs – such as replacing titanium for waste tubes, metal for storage tanks and metal-based toilet assemblies, according to Böttger and Wedler.

“Additionally, since 1977, the galley waste disposal units of various suppliers enable the disposal of small – partly – liquid galley waste directly into the aircraft’s waste tanks. Diehl Aviation’s Galley Waste Disposal Unit (GWDU) is an innovative aerosol-air vectoring injection system, featuring a specific industrial design approach with a one-box architecture.

“The GWDU facilitates the disposal of a high amount of waste. For instance, the GWDU is able to dispose more than 1lbs coffee powder in a single flush. Not only the galley personnel profits from the speedy disposal, but also the airline due to the saving of rinsing water and thus of weight with each individual flush,” they say.

Attending the needs of airlines

Airlines have specific needs with respect to WWS which are being increasingly attended by the manufacturers of WWS. According to Canagassabe, the most important challenge for the Air France KLM fleet is the reliability of the waste system, particularly the vacuum waste system.

“Poor reliability on this system will affect aeroplane operations (for example flight delays) and maintenance (such as additional unscheduled operations),” he says. “This also a challenge for many other operators.

Boeing is still working on improvement and releases regular updates to inform operators about specific maintenance intervals, good maintenance practices, and equipment reliability. These are based on their own analysis and on the operators’ experience.”

“Given that WWS is not visible to passengers, the key requirements for airlines are reliability and the overall cost of operation. With legacy products, blockages and failures occur more frequently. These occurrences cause a negative passenger experience if a lavatory is blocked inflight or if a system fails without readily available spares to support,” says Khaled.

Blockages occur due to objects falling into the toilets and the amount of built-up limescale increasing in the vacuum waste system (waste line condition). Often the combination of both events raises the risk of blockages. The challenge is to determine the correct cleaning intervals for the waste line cleaning.

“The condition of the waste line does not only depend on the flight hours of an aircraft, but also on the number of passengers, the duration of the flight and the flight route,” says Winkler.

“To determine the condition of the waste line, the system has to be opened and inspected visually. Unfortunately, it is not possible to simulate the real use of an aircraft toilet system in a mock-up on the ground.”

“However, we are currently doing a research project with a partner university to identify parameters that indicate the real-time scale in the vacuum waste lines. We expect to publish the results of this project in the spring of 2019.”

“To avoid misuse of vacuum toilet system that causes blockage of waste tubes (for example due to diaper removal in toilet bowl) or disruption of waste tube and waste tanks (such as due to impact effects of accelerated objects like bottles or batteries), WWS suppliers have committed significant effort to investigating waste tube and tank material and system stability. For instance, the development of impact absorbers in waste storage areas was essential in order to avoid serious damage of the system,” say Böttger and Wedler.

In addition to the general reliability requirement, certain airlines experience different needs based on their maintenance practices and business models.

“Maintenance and cleaning practices differ from one airline to another and insufficient cleaning causes premature system failures. With the ever-increasing cabin load factors combined with record flight durations, airlines are also becoming more sensitive to water volumes and consumption, for example. Products that consume less water are well perceived in the industry,” says Khaled.

“WWS suppliers work with original equipment manufacturers to design and manufacture solutions that are resilient to these various practices and regions. While the majority of legacy in-service fleets have less modern equipment, airline needs can be addressed on newer platforms, or through retrofits by embedding intelligence into the system controller and smart devices that eliminate single-point failure, ensuring real-time communication and providing diagnostics.

“While these new features can improve reliability, regular WWS cleaning practices remain one of the biggest contributors to good durability.”

Böttger and Wedler comment: “Airlines generally focus on cost reduction for scheduled and unscheduled maintenance. In order to keep the maintenance costs low, the manufacturers attend this need by increased reliability of equipment and therefore extended service intervals for the airliner.

“Additionally, the manufacturers are focusing on smart equipment (such as the motor-valve or solenoid valve with serial bus system, etc.) to facilitate the daily service of the potable water and waste-water system for the operator.”

“On top of that, the airlines need to know the exact system status and improved fill level of waste and water. Therefore, manufacturers focus on improving the level measurement accuracy of the potable water tank and an improved level measurement technique of waste-water storage. At the same time suppliers are working on the development of easy-to-use indication panels, capable to control and indicate level over a wide range in order to react faster and facilitate the work.”

Increasing complexity

Due to smart equipment system complexity is increasing continuously. Although this reduces the work of operators due to automatic reports, in order to carry out the maintenance of these complex systems qualified service personnel is essential.

“Previously, fault finding was easy with simple mechanical levers and valves but more advanced software-based systems, such as UV sterilisers, need a display unit with menu options to investigate faults. In addition, maintenance personnel needs to have at least a basic understanding of the technology involved,” say Böttger and Wedler.

Khaled believes that legacy systems without diagnosis tools require highly skilled and technical personnel to troubleshoot and address failures. “WWS are becoming more complex in order to simplify serviceability and maintainability to the end-user through connected Smarter WWS.

“These smart devices self-diagnose and pin-point failures within WWS, thereby minimising the requirement for highly skilled technicians needed for servicing,” she says.

“Maintenance activities can be proactive and predictive, resulting in quicker turnaround times for airlines, as real-time trend diagnostics are provided by WWS to the cabin management system and available to be downloaded.”

“Systems are becoming more convenient, but also more complex. WWS varies depending on the type of aircraft. Maintenance procedures are becoming increasingly complex. Therefore, more special tools and skills will be required in the future. Manufacturers should establish appropriate standards to limit the variety and complexity of WWS,” says Winkler.

Right water amount

For airlines, it is often a challenge to determine the right amount of potable water to carry on board. Not only the duration of the flight but also the number of passengers, possible delays and the availability of potable water at destinations on the route have to be considered.

“Furthermore, the flight crew must be on board before the water is serviced, in order to set the system to the desired pre-selection. The preselection is reset automatically to the manufacturers’ default after each servicing,” says Winkler.

“The potable water system provides real-time water tank level sensoring to the aircraft. Typically, airlines fill the water tank completely independently of the expected load factor. To reduce fuel consumption, airlines can adjust the water volume to the number of passengers being carried and the applicable flight duration,” says Khaled.

Winkler believes that it would be very useful if the system manufacturers implemented a preselection preferred by the customer, which is automatically kept after resetting and switching on the system.

“It would also be useful to have a provision for reducing a full potable water tank prior to departure, remote from the cabin. This would enable the take-off weight to be reduced in accordance with the final passenger requirements,” he says.

“Airlines can have a high impact on further technologies by supporting suppliers on investigations and experiments on waterless applications, such as a waterless pissoir or on greywater reuse technology. One focus is the reuse of sink water for lavatory flushes.

“In addition to this, the airlines should generally sensitise passengers to economically use water, like in the number of flushes or instance of the hand-washing time,” conclude Böttger and Wedler.