Michael Doran explores a core element of cabin air quality

This article originally ran in the July/August issue of Aircraft Cabin Management, and is presented here as one of out ’12 Features of Christmas’ 

In what must surely be one of the greatest paradoxes of aviation, the passengers at the back of the plane are generally breathing better quality air than ones sitting in the first-class suites up front.
That does not apply if you are on an Airbus A350, a Boeing 787 Dreamliner or an aeroplane that has been fitted with an environmental control system with humidity control. Without that, the driest part of the aircraft is in first class with 5-8% relative humidity, compared to 7-10% in business and 10-15% in economy.
The situation is worse on the flight deck and in the crew rest areas where humidity can be below 5%, making these critical areas dryer than any place on Earth. The systems on the A350, 787 and 777X address both those sections, while other aircraft types can be retrofitted with humidification units.

Discomfort & dehydration
Most people find that a relative humidity of 30-60% is comfortable which is why low humidity onboard can cause discomfort, including dry skin, irritated eyes and dehydration. The issue is that the air ingested into the cabin at cruising altitude has no humidity and therefore only source of humidity is the people travelling on the aircraft.
The area with the most people is where the air will have the highest humidity, which is why the air down the back is more humid than in the first or business class, the cockpit or the crew rest area. As flight sectors get longer, airlines are becoming more concerned about the wellness of all onboard and are turning to experts such as Sweden’s CTT Systems.
CTT Systems provides moisture control systems to combat the two main moisture-related problems in aviation – too much or too little moisture in cabin air. Too little will leave passengers affected by dehydration and too much will add extra weight to the aircraft and increase fuel consumption.
The CTT Inflight Humidification (IFH) system adds moisture content via the aircraft ventilation system by using purified water from the aircraft’s water supply to evaporate dry air through a humidifier pad.
CTT humidifier products have been in-service since 2007, including on A350s, A380s and 777s, and are now the de-facto standard for flight decks on long-haul widebody aircraft and standard in rest areas on the 787 and some A350s.

Air India first
Last year Air India incorporated CTT’s Humidifier Onboard system to the business class cabins of its new A350‑900s. Air India is the first airline in Southeast Asia and the Middle East to commence flights with humidification in business class that will bring the humidity from 5-7% in the front cabin to a ground like level of 20-23%.
At the time, Ola Häggfeldt, chief commercial officer at CTT Systems said, “We congratulate Air India for commencing operations with the first A350-900 aircraft with a leading-edge interior. Humidifier Onboard transforms the business class experience beyond comfort into true wellbeing by generating humidity at a healthier level.”
The A350 has had great success over the last few years and a significant part of that is due to the enhanced comfort of its Airspace cabin. Features such as reduced noise, mood lighting, draft-free ventilation, multiple temperature zones and a lower cabin altitude of just 6,000 feet all combine to reduce the effects of long-haul travel.
When Dreamliners were introduced, much was made of the cabin environment and the mood lighting that would leave people feeling more refreshed and less jetlagged. The evidence is clear that increasing cabin humidity also contributes to wellness so it’s no surprise it’s being addressed in the premium cabins.
CTT believes that by restoring cabin humidity passengers will feel more balanced, at ease and hydrated, ensuring high quality sleep and reduced jetlag. The pandemic made airlines think more about wellbeing and the quality of the air in the cabin so it follows that humidity levels are gaining more traction.
Dry air can play havoc with our immune systems as dried out nasal membranes are more likely to be penetrated by viruses, with studies showing that as many as 30% of passengers contract some form of sore throat or similar infection within five days of a flight.
Airlines spend a lot of time designing meals for premium cabins and they know these meals will taste differently at 30,000 feet than in the catering kitchen. This is also affected by humidity as when the nasal cavity dries out the sense of smell is diminished, with experts revealing that up to 80% of what we consider taste is actually derived from smell.

When humidity is too high
The second moisture- related issue is that when cabin air is moist, water accumulates in the insulation blankets between the cabin lining and the fuselage. Despite the cabin’s relatively dry air, the low moisture content can condensate on the cold fuselage surface.
That accumulated moisture can add between 200 to 400 kilograms to the aircraft and significantly increase fuel consumption and carbon emissions. An extra 200 kilograms of weight on a standard passenger aircraft means 21 tons more fuel is needed while CO² emissions increase by 66 tons each year.
The CTT Anti-Fuselage-Condensation system removes trapped water in the blankets, keeping the crown area dry and preventing excess weight from water accumulation. The reduced humidity in the intermediate space also means that electronic equipment does not need as much maintenance.
In the CTT system, moist air is passed through a dehumidifying turbine and out through piccolo ducts routed along the length of the crown area to create a dry air barrier. The process protects the aircraft from corrosion and allows airlines to operate with lower energy needs and fewer emissions.
In February, low-cost carrier Jet2.com confirmed an order for systems to be retrofitted to146 Airbus A321neos, with optional rights for a further nine systems. As an existing customer since 2007, Jet2.com has already fitted more than 100 Airbus and Boeing aircraft with the anti‑condensation system.

Wellbeing on Qantas
Australian airline Qantas has chosen modified Airbus A350-1000s for its ultra-long-haul Project Sunrise services, due to start in 2027. These nonstop flights will spend around 20 hours in the air, making passenger wellbeing a priority.
Airbus senior vice president marketing, Joost van der Heijden says, “The A350 Airspace cabin has been designed to provide passengers with the best possible flight experience, including the highest air quality, more personal space, the quietest cabin in the sky and full connectivity throughout.”
Last year Qantas released details of its new interiors which include six first class suites. The enclosed suites feature a master control panel that will set personal temperature and humidity levels.
In 2019, Qantas operated three Project Sunrise research flights from New York and London to Sydney with researchers onboard to monitor volunteer passengers fitted with wearable devices. These volunteers followed a specially designed menu and lighting, sleep and movement sequences to test the likely impact of the inflight optimisations.
Those learnings were used to design the interiors for the Project Sunrise A350s, which are configured to carry just 238 passengers compared to the usual 300+ seat layout. Some of the extra space has been used to create the Wellbeing Zone located between premium economy and economy cabins to promote movement, stretching and hydration.