Fresh air for the passenger experience

When considering environmental factors in commercial aerospace, the most familiar themes focus on the reduction of emissions, noise, and fuel consumption. These design factors are interlinked and present a substantial technical challenge for designers and manufacturers, who must also ensure that aircraft are attractive to operators and their customers.

Some firms focus on modifying factors less-obvious than weight and emission; factors that can nevertheless make a difference as a byproduct of introducing an enhanced cabin environment for passengers. Countering internal condensation with a humidification system is one such example.

Sweden-based CTT Systems works with major commercial aircraft manufacturers and many specialist completion and maintenance companies around the world in providing humidity-control products and anti-condensation systems. These systems are designed to prevent moisture issues in aircraft and to enhance the in-flight comfort of crew and passengers.

In for the long haul

The human body can tolerate wide variations in humidity, but on a long-haul journey, flying at a high altitude, the air quality in a passenger jet cabin can deteriorate very quickly. Cabin air can reach desert-like, arid conditions within an hour after takeoff and the effects can often be noticed soon after the aircraft levels off into its cruise phase, typically at 35,000 to 40,000 ft. Symptoms often include dry skin and eyes, difficulty sleeping, and cold or allergy symptoms as the linings of the mouth and nose dry out.

Humidifiers designed by CTT are based on evaporative cooling technology that improves air quality and effectively precludes the transfer of bacteria by reducing particles in the cabin air.

Dramatic condensation can occur as each passenger exhales an average of 100 gm of water per hour. If this condensed water is not drained from the aircraft, the effect can be noticed by passengers during takeoff and landing when water on top of ceiling panels seeps down into the cabin, causing “rain in the plane.”

When water works its way into the cabin insulation panels, the insulation effect is reduced and the weight of a large aircraft can increase by over half a ton, depending on the aircraft type, passenger load, and other operational factors, such as climate. This results in higher fuel consumption and associated environmental impacts.

Clearing the air

According to CTT, providing moisture removal systems that use established industry technology can address the root causes of in-flight condensation. The CTT Zonal Drying System removes cabin air moisture by directing air from the crown area or cargo spaces to zonal drying units located at strategic points in the aircraft. Special ducting then circulates this dry air between the outer skin and cabin. This lowers the dew point in the crown area preventing the condensation process from taking place and keeps the insulating blankets dry.

A four-pole inlet fan feeds two separate airstreams into a rotor impregnated with silica gel, which absorbs humidity from one of the air streams and processes it before releasing it as dry air. Electric heaters warm up the second air stream before it enters the rotor. As it passes through the slow-moving rotor the heated air absorbs humidity collected from the processed air. The regenerated air is then fed into the aircraft recirculation system, or dumped through an outflow valve. The system is activated when the aircraft is powered up.


CTT’s CAIR system offers higher levels of passenger comfort through providing fresher air, which can deliver an edge in a highly competitive global airline market. The introduction of such features as flat-bed seats, on-demand TV, and internet access has provided additional benefits to attract premium customer loyalty, but enhancing the supply of fresh air is a very tangible improvement that more discerning frequent fliers are now appreciating.

This post is based on an article by Richard Gardner for Aerospace Engineering magazine. For the complete article, visit