Aircraft Filtration


The quality of aircraft cabin air has received increasing attention over the years given its impact on crew and passenger health, and aircraft manufacturers and operators are installing advanced cabin air filtration systems to provide ‘clean’ air in aircraft cabins.

The emphasis on aircraft cabin air quality has gained prominence due to fume events and the detrimental impact on the health of aircraft crew and passengers from the associated toxic aerosol/VOC contaminants.  The aircraft and engine OEMs, industry standards organizations, and regulatory agencies are focusing on assessing and improving cabin air quality.  Advanced cabin air filtration systems are being adopted by aircraft OEMs, and airlines and operators.   Development is also under way to identify fume events and provide total air filtration (100 % of the air) in the cabin to mitigate serious consequences associated with fume events.

Another area of interest is fuel tank inerting systems (FTIS). The sensitivity of air separation membranes/modules to contaminants such as aerosols, Ozone, VOCs and particulates has resulted in reduced air separation module (ASM) service life.  The development of multi-stage pre-filters to remove the above contaminants and extend ASM service life is actively being pursued by the industry.

The innovative Pall filtration technologies for the above air systems on-board aircraft are discussed in this article.

Cabin Air Filtration

Cabin air is comprised of approximately 50 % re-circulated air mixed with 50 % air from either the engine bleed air or external air processed through a compressor system.  Contaminants that could be present in cabin air are: particulate contamination, including biological contamination (bacteria, viruses, bio-effluent); aerosols from low volatility fluids such as engine lube oil or hydraulic fluid; volatile organic compounds (VOCs), including odors,  from the airport environment, de-icing fluid, or passenger sources (food, perfumes); and contaminant gases (e.g., carbon dioxide).


High-Efficiency Particulate Arrestance (HEPA) Filtration

Pall was a pioneer in introducing High-Efficiency Particulate Arrestance (HEPA) filtration for cabin air in the 1990s when air recirculation was introduced in cabin air systems.  These filters are rated at 99.97% particle removal efficiency for particles in the 0.3 µm size range, considered the most penetrating particle size. and, in addition to crew and passenger protection, also protect air system components such as the recirculation fan from wear and particulate induced damage.

Carbon as an Adsorbent

Removal of VOCs is accomplished by incorporating an adsorbent such as carbon which removes a wide range of VOCs.  Traditional carbon adsorbents are manufactured from coconut shells and have been integrated in cabin air filters for controlling VOCs.  Pall has worked with a manufacturer of carbon adsorbents to design a custom carbon adsorbent for the application which has higher adsorption efficiency as well as higher VOC capacity compared to traditional carbon adsorbents.  These advanced cabin air filters (Pall A-CAF) replace legacy filters and exhibit higher capacity and performance in removing VOCs and odor-causing compounds.


A-CAF Filtration

Retrofitting an aircraft with A-CAF adds negligible cost versus HEPA-only filters, yet fume events requiring flight alterations cost from $10,000 to $200,000, not including incalculable reputation damage.

Fuel Tank Inerting Systems

In 2008, the FAA required operators and manufacturers to incorporate a Flammability Reduction Means (FRM) to inhibit fuel ignition in fuel tanks having a flammability exposure exceeding certain thresholds. The rule affects new aircraft types, new aircraft in production and in-service aircraft produced after January 1st, 1992.

To accomplish the above, the fuel tanks are inerted with Nitrogen rich air (< 12 % Oxygen in the fuel tank) produced by passing the engine bleed air or outside air through an Air Separation Module (ASM). The ASM contains membranes which separate Oxygen from the air thus producing a Nitrogen rich inerting air stream.

The membranes used in ASMs are organic membranes that are susceptible to performance and/or physical degradation due to moisture, aerosols, Ozone, VOCs and particulate contamination.


Four-Stage ASM LEF (Life Extension Filter)

Pall has developed an ‘industry first’ advanced four-stage ASM prefilter life extension filter which incorporates a coalescer for removing moisture/aerosols, a catalyst for removing Ozone, a custom Carbon adsorbent for removing VOCs, and a HEPA rated particulate filtration medium.

Pall Partnerships

Pall has a 75-year history in innovation of filtration technology for Aerospace.  Pall scientists and engineers conduct applications research, often working with OEMs, Fluid System Integrators, and end users, including the military, to produce new filtration technology for solving challenging problems.   As part of this research, analysis of serviced filter elements from operators provides valuable information on the type/quantity of contamination loading the filter elements.

In addition to providing diagnostic insight into the fluid system operating condition and prognosis of potential component malfunction/failure, this also allows for the design of filter elements for optimal service life in the actual application based on the operator maintenance cycles.

Pall Aerospace has extensive OEM relationships with aircraft manufacturers, such as Airbus and Boeing, and engine manufacturers such as Rolls Royce, Pratt & Whitney and GE Aviation. Pall also has a 27-year partnership with Satair as the official Pall commercial aircraft aftermarket distributor.  Pall Aerospace works closely with the OEMs in developing filtration systems for new platforms and with the airlines and operators in solving contamination control issues in aircraft fluid systems.

For more information on aircraft filtration, purification and separation solutions: