How does the cabin air system work?

On aircraft, cabin air quality contributes significantly to the comfort and well-being of passengers and crews alike. But what is cabin air quality, what is the importance of cabin air quality in aircraft design and operation, and what does Airbus do to ensure good air quality in the cabin? Let’s take a journey into the technical depths of “cabin air quality”. 

Transforming outside air into a comfortable cabin climate 

Cabin air system

At cruise altitude (10,000 m), the air is very thin, very dry and very cold (-50°C). The pressure is less than one fifth of normal ambient pressure and the human body cannot absorb enough oxygen in this condition to survive. Hence, the air ventilation systems need to transform it in order to provide regulated fresh air with adequate temperature, pressure, oxygen and humidity.

Modern passenger aircraft flying at cruise altitude must  operate in a very hostile environment. Flying at an altitude of 10 to 13 kms ensures the most efficient, fuel-saving and smooth flightpath. But a human being would not be able to survive in such conditions, which are harsher than on the top of Mount Everest.

A passenger aircraft must also function at the opposite extremes, including when parked at an airport in hot desert or tropical regions. There, the  aircraft’s ventilation system must cool down the cabin to an acceptable level of comfort. This means that the air conditioning in an aircraft must be extremely reliable and flexible. Development and testing of the air supply system is a key element in developing a new aircraft. In addition to reliability and redundancy, comfort is extremely important.

The ideal blend: fresh external air and optimised recirculation 

The cabin air in Airbus aircraft is a mix of fresh air drawn from outside, and recirculated air that has been filtered to remove particles in the air as small as microscopic bacteria and virus clusters.

Mixing external air and recirculated air contributes to the efficiency of modern passenger aircraft and helps reduce fuel consumption and resulting pollution. It would be possible, from a technical point of view, to use only outside air. But this would increase fuel consumption and production of carbon dioxide. Efficient filtering improves cabin air quality while contributing to more sustainable operations.

Rapid air renewal: a complete cabin refresh every three minutes 

Air in Airbus cabins is replenished about every 2-3 minutes in normal operations. Conditioned air enters the cabin via air inlets near the cabin ceiling and leaves at floor level. At seat level, there is a constant downward wash of air at 1 m/s.

Even without the use of some recirculated air, the air in Airbus cabins is replenished every 2-3 minutes. This ensures continuous removal of viruses and other particles. In addition, passengers and crew are supplied with fresh, clean air.

Airflow in the cabin follows a pre-defined and well-tested pattern. It enters near the ceiling and then flows to the floor, where it is sucked into the lower area of the aircraft before being dumped outboard or moved to the filter system for recirculation.

The development of the cabin air system and the flow pattern is one of the most critical parts in the design of new aircraft. Beside the reliable air supply, the system is also key for comfort - air that is too hot or too cold, too dry or too humid, can be uncomfortable for passengers and crew members. 

HEPA filter aircraft cabin

Hospital-Grade HEPA filtration: eliminating 99.9% of airborne particles 

The HEPA filters used in Airbus aircraft remove more than 99.9% of micro- and nano-particulates, viruses and bacteria. None of the air that is supplied to aircraft toilets, galleys and cargo-holds is recirculated into the cabin – it is dumped directly overboard.

Filters used for aircraft air conditioning are similar to the ones used in hospitals. They remove micro- and nano-particulates, bacteria, and viruses.  A dedicated maintenance protocol requires operators to check and change these filters at specific intervals to maintain the designed airflow. In addition, many aircraft are equipped with ozone converters to remove ozone from the air before it enters the cabin. 

Air supply to aircraft toilets, galleys and cargo-holds is directly dumped overboard to avoid distribution of unpleasant odours and, in case of a fire in the cargo-hold, prevent distribution of smoke.

HEPA Filters are used to remove extremely small particles like viruses, but, on their own, cannot remove odours (for example when on ground during pushback or taxiing behind another aircraft, some smells might be ingested.) A specific kind of filter has been developed that includes, in addition to the HEPA layer, an activated carbon layer enabling odour removal. 

Aircraft cabin air flow

Setting the standard: exceeding stringent airworthiness regulations 

Airbus aircraft design meets or exceeds compliance with airworthiness regulations to provide the highest level of cabin air quality, and is designed to prevent air contamination under normal operating conditions.

Airbus is required to - and does -  follow the high standards imposed by independent airworthiness authorities worldwide. Test and qualification covers the engine and the bleed air system. By a series of runs in a testbed, it has to be proven that the level of various  compounds in the air is below critical standards or that there is even no contamination in the flow of air. 

Ongoing collaboration and research into passenger wellbeing 

Airbus works with its industry partners and regulatory authorities to continually examine all aspects of the cabin environment.

For decades, Airbus has been working with scientific partners worldwide to examine all aspects of cabin air quality. This is reflected in Airbus’ participation in numerous research projects, including under the lead of EASA and of major scientific institutions in Europe.

Airbus is also carefully monitoring institutional and independent studies, as well as technological advances, and continuously reviews whether any sensing, air filtration or cleaning technology could add value to passengers, crews and aircraft operations. The air provided to the cabin during flight is already very clean under normal operating conditions, and the introduction of further technologies needs to be justified and carefully considered against technical and environmental repercussions.

Research on cabin air quality requires highly specialized and sensitive equipment, in combination with extremely qualified scientists in a wide range of areas including engineering, physical science and toxicology.