The prospect of having to modify aircraft cabins in order to reduce the infection risk during flights will likely be another headache for cash-strapped airlines battling to survive the coronavirus crisis.

However, Diehl Aviation sees an opportunity to respond to passenger health concerns with new products and, the German systems and interior equipment manufacturer argues, for airlines to differentiate themselves as they vie to attract customers back on board.

Amid the pandemic, Diehl has started developing – or accelerated previous work on – products aimed at improving onboard hygiene, most of them retrofitable. The plan is to make them available later this year or in 2021.

Senior vice-president product innovation Helge Sachs tells Cirium that the company is developing a UV-C lamp to disinfect lavatory surfaces. The lamp is designed to be fitted to lavatory sidewalls with a telescope arm for temporary deployment either on the ground during aircraft turnaround or by the crew during long-haul flights.

The lamp will operate with a light frequency that poses a health risk for humans and thus be installed only by staff when required. With a cleaning cycle of up to a minute, the lamp’s operation will be automated to ensure that no person is present in the cubicle during exposure. Otherwise, the equipment would be stowed away for use when required.

Additionally, Diehl is working on ways of employing UV light in the cabin – with light frequencies that pose no health risk – to reduce contamination on interior surfaces. One of the options is to install a UV light source in the passenger-service units above the seats to reduce contamination on exposed surfaces such as seat cushions, armrests, fold-down tables, and IFE equipment.

Another option is to emit UV light via the regular LED cabin-lighting system. Sachs says Diehl is working on the required control-software updates.

UV light has been in regular use for water purification in ground-based supply systems for years, and the same principle has been used to provide potable tab water on business and VIP aircraft. Now, Diehl indicates that it is studying the wider use of such equipment on passenger aircraft.

Sachs foresees that the UV light solutions will become available for service in 2021. Meanwhile, the company is offering lower-tech solutions – including disinfectant dispensers, face-mask containers, cautionary cabin placards – and accelerating development of retrofitable, touchless controls for lavatories and other passenger service equipment.


Airlines and aerospace manufacturers, including Diehl, have argued that the risk of infection on board aircraft is, in principle, lower than for many other enclosed public spaces and public transport modes. One cited reason for this is that in cabins, air flows vertically from air-conditioning outlets above the passenger seats to extraction points near the floor – which should reduce the spread of aerosols across the cabin.

The air of an entire passenger cabin is typically recycled every 2-3min, and filtered by hospital-style HEPA filters. Sachs acknowledges that hospital air will have an edge in purity terms over aircraft cabins because ground systems have an unlimited supply of fresh outside air, which is more restricted in pressurised cabins at altitude.

Sachs says the infection risk on board aircraft is significantly lower than in other busy, enclosed public spaces. But he believes more can be done to improve onboard hygiene and passenger wellbeing.

Multiple airlines have mandated passengers to wear mouth-and-nose covers from the time of boarding until after disembarkation, in addition to keeping within other restrictions and guidelines. Sachs suggests that this might be acceptable to passengers on short- and medium-haul, but expresses doubt those flying long-haul will accept having to wear face masks, and suggests that such a requirement could have an impact on demand.

Since the onset of the pandemic, several interior equipment manufacturers have proposed installation of screens between seats or cabin-layout changes, such as alternating forward- and rear-facing seats, to increase passenger separation. Sachs dismisses these ideas, arguing that additional physical barriers and seat enclosures will be “psychologically not acceptable” for travellers as aircraft cabins already represent quite a confined space for the vast majority in economy class.

But more importantly, Sachs believes that barriers between seats will not be certifiable because they could restrict passenger access to oxygen masks and impinge on cabin-evacuation requirements. This is the reason, Sachs believes, that airframers have decided not to pursue seat-divider proposals published over recent months.

In June, US design agency Teague published a proposal to create a “curtain of air between passengers” to limit the spread of aerosols. Under the “AirShield” initiative, the Seattle-based company – a long-standing Boeing partner – developed a new “low-weight, easily retrofitable” fresh-air nozzle for the PSUs commonly found on many though not all passenger aircraft.

“The shape and speed of the air created by AirShield is optimised to deflect particles emitted from one passenger downward, safely away from other passengers’ noses and mouth,” Teague says in a note on the proposal.

Diehl is pursuing a similar approach based on the same principle of creating distinct downward airflows around passengers to contain and extract aerosols. But Sachs believes the air pressure from regular fresh-air nozzles is too low to create the desired effect – indicating perhaps that Diehl is looking to change the fresh-air flow pattern of the overall cabin air-conditioning system.

The manufacturer wants to “optimise [cabin] air circulation and humidity”, it says. Sachs declines to provide more detail at this point, citing competitive concerns. But he says Diehl’s in-development system will be a modification that can be installed in overnight checks with “minimal invasion” and won’t be costly for airlines. Diehl intends to have the system ready for service entry by year-end, he says.

Additionally, Diehl is exploring options to increase cabin air humidity because, Sachs says, a relative humidity above 40% “significantly” reduces infection risk of virus transfer.

Humidity levels in aircraft cabins vary depending on passenger density because occupant breathing and transpiration and the vaporisation from hot food and drinks are the only moisture sources as outside air at 40,000ft has a relative humidity of less than 1%.

In economy class, relative humidity typically ranges between 10% and 15% without active humidification, while it can drop as low 5% in premium accommodation. Relative humidity in natural environments depends on the geographical location and season, but typically varies between 15% in deserts to over 90% in tropical regions.

Active cabin-air humidifiers can raise relative humidity to around 20%. Their use will also require installation of zonal drying equipment to avoid condensation and related issues, such as excessive weight through water accumulation and potential mould build-up.

Several airlines have optionally equipped aircraft with humidifiers – especially newly delivered long-haul jets – in order to boost moisture levels in specific areas, notably premium seat sections, flightdecks and crew-rest compartments. But the vast majority of passengers have not come to enjoy benefits of active cabin-air humidification. Some airlines have even installed drying equipment on its own to reduce regular condensation issues, without humidifiers.

Sachs thinks that increased cabin air humidity could become a specific objective for next-generation aircraft. But he notes that such aircraft would need to be “insulated differently” to avoid condensation issues. Noting weight concerns for existing humidifier and drying equipment and the water required to humidify cabins – Diehl is a supplier of such systems, alongside other manufacturers – he says he sees limited scope to retrofit in-service airliners with such systems.


Sachs acknowledges that airlines will think twice about marking large investments in cabin-interior changes, especially in the current environment where carriers are fighting for survival and many depend on state aid to secure future operations. In his view, however, the post-crisis recovery presents a classic chicken-and-egg dilemma between investment and revenue, as current measures like mandatory face masks and procedural changes for boarding and onboard service may not be enough to sustainably attract passengers back into the air – beyond pent-up seasonal holiday demand – especially if further virus outbreaks occur.

“We firmly believe that airlines want to differentiate themselves,” Sachs says. He suggests that the post-Covid-19 recovery represents an opportunity for airlines to build new customer loyalty and that carriers seen to make an effort to improve passenger wellbeing might win their approval. He acknowledges that airlines are unlikely to make huge investments in new equipment, but says the objective is to find a “sweet spot” between costs and noticeable benefits. Sachs says a C-suite at one airline indicated that, were the crisis to result in new cabin-industry standards, it wanted to be the first to bring compliant equipment to the market.

Diehl, he says, sees the crisis as an opportunity to introduce new products, and the company intends – using branded placards and equipment – to raise the travelling public’s perception of it as an innovator in aircraft cabins.

Sachs believes the pandemic will spur substantial changes in cabin equipment and layouts in the longer term, especially for widebodies. A central objective will be to improve cleanliness because aircraft interiors cannot practically have deep cleans after every single flight despite being occupied by hundreds of passengers and crew. Sachs foresees a new generation of cabin interior with a minimalistic, Scandinavian-style design featuring fewer cavities, nooks and crannies that are difficult to clean, and simply less material that can be contaminated.

Fewer, brighter colours and generally more white surfaces might become more dominant, while employment dirt-repellent and self-cleaning surface coatings will play a large role in future interiors, he thinks. Cabin air flow can be optimised to reduce contamination, and Sachs sees room for further improvement of air quality with additional filters.

Sachs is aware that the premise of making aircraft interiors cleaner might reduce opportunities for airlines to differentiate their cabins and express their corporate identity through conventional choice of cabin equipment – seats, furnishings, monuments, crew uniforms, in-flight catering utensils, etc.

He suggests, however, that increased hygiene will become much more relevant in aircraft because of the pandemic – and the conventional wisdom of simply increasing the use of cleaning detergents and staff is “not the way forward”.

This analysis was written by Michael Gubisch, part of Cirium’s London-based reporting team