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Airliner Filtration Essential to Commerce and Safety

Air carriers have a keen interest in onboard air filtration systems.

Over several decades airline manufacturers have steadily improved the technology of maintaining clean cabin air, which is essential for both passenger and pilot safety. More recently, filtration has been mandated as part of Fuel Tank Inerting Systems (FTIS), which depend on pure nitrogen extraction from engine bleed air.

Air contaminants include particulates and Volatile Organic Compounds (VOCs), which in high concentrations can create toxic fumes. Several filtration stages combine to guard against costly fume events, which when unresolved require turn back or diversion of a plane about to take off, or worse, of a flight already in progress. Similarly, FTIS uses methods comparable to cabin air filtration to maintain a non-flammable, oxygen-free buffer in fuel tanks to reduce explosion risks.

Filtration methods aren’t as simple as it might appear at first glance. Understanding how filtering technologies work is critical for both air carrier management and MRO providers. Once understood, air quality problems can be mitigated before they impact safety or revenue.

Cabin Air Filtration

Ensuring clean cabin air is a challenge, because cabin air has two sources: 50% originates with engine bleed air to maintain cabin pressurization, and contains VOCs and other contaminants, while the other 50% is recirculated air that picks up particulates and odors from the passenger compartment. Filtration has advanced significantly over recent years, both as a result of extensive R&D by Pall engineering groups, as well as a desire from OEMs and operators to keep improving the quality of air onboard aircraft.


Engine Bleed Air

Traditional engine bleed air filtration uses natural-fiber-based (typically coconut husk) filtration media, which has a large surface area for removing VOCs and odor-causing compounds. Contaminants saturate this media over time, requiring replacement during regular MRO intervals, an expensive service task.

Recirculating Air

Recirculating air systems introduced in the 1990s were High-Efficiency Particulate Arrestance (HEPA) filters based on technology developed for hospitals to remove airborne infectious agents. These systems also protect recirculation fans from contamination and particulate damage, as they have a 99.999% microbial removal efficiency. They do not, however, remove unhealthy VOCs that enter the cabin via engine bleed air.

Retrofitting an aircraft with A-CAF costs roughly $10,000, while fume events requiring flight alterations cost from $10,000 to $200,000, not including incalculable reputation damage.

To reduce these service events, and further improve air quality, many aircraft now incorporate the Pall Advanced CAF (A-CAF) systems focusing on VOC and odor reduction. A-CAF systems replace legacy “natural” filtration media with advanced synthetic carbon media. Synthetic carbon is superior to traditional natural-fiber filtration media because it has a larger surface area with smaller pores, giving it a higher capacity and performance in removing VOCs and odor-causing compounds. Synthetic carbon also has longer endurance, reducing media change intervals, which provides more predictable performance — essential to heading off fume events. As a result of A-CAF deployment, the number and severity of fume events has dropped to the point where the systems pay for themselves.

Nitrogen Generating Systems

Fuel Tank Inerting Systems

A recent safety requirement for all modern air carrier aircraft is fuel tank inerting, which replaces oxygen-rich air that normally fills unused space in fuel tanks with non-flammable nitrogen gas. This air quality requirement goes unnoticed by passengers and crew, but it is critical to flight safety. In 2008, the FAA required operators and manufacturers to incorporate a Flammability Reduction Means (FRM) to inhibit ignition on 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, and thus has had a huge impact on MRO operations.

The source for FTIS nitrogen is engine bleed air, which passes through an Air Separation Module (ASM) to remove oxygen and supply pure nitrogen. This nitrogen then replaces the air above fuel in the tanks, thus removing the oxygen required for combustion, eliminating explosion hazards within the tank.

However, the ASM, fuel system and tanks are sensitive to water and VOCs, which degrade ASM performance and risk tank corrosion and fuel contamination. To avoid damaging the expensive ASM component or contaminating other systems, engine bleed air must be filtered to remove liquid aerosols and particulates.


Pall has developed an advanced four-stage ASM filter, which removes aerosols and particulates but also removes ozone and Volatile Organic Compounds (VOCs).

Four-stage filtration increases ASM life and reduces the possibility of inflight failure that could create a fuel system hazard.

Because the ASM is a recent introduction to aerospace environments, it must be retrofitted into existing aircraft based on an aircraft Supplemental Type Certificate (STC). Filter media components must also be supplied in compliance with either an STC or Parts Manufacturing Authority (PMA). Pall has both STC- and PMA-certified NGS filter media parts and manufactures them in quantities that meet the existing, and growing, need for NGS deployment.

75 Years of Innovation

As an R&D and manufacturing entity, Pall has a 75-year history in production quality and MRO support through consumed filter analysis. Analysis results help air carriers tailor their filtration maintenance cycles to achieve the most life out of each filter. The analysis also provides early warning of changing conditions, which can guide future maintenance plans.

Pall has extensive OEM relationships with aircraft manufacturers, such as Airbus and Boeing, to ensure parts compatibility, as well as to anticipate new part requirements. Getting parts into the field, and consumed filters back from carriers requires a vast, but reliable, distribution network. Pall has a 75-year partnership with Satair as our conduit to carriers, with on-time fresh filter delivery and RMAing filters back to Pall for its analysis program.

Efficiency, Safety, and Profitability
Pall is the worldwide expert on air filtration technology for the aviation industry, both commercial and military, with thousands of patents and an $80M annual R&D budget. Pall’s A-CAF systems provide carriers best-of-breed protection against the costly impact of highly public fume events. And Pall’s advanced four-stage ASM filtering system meets global FTIS regulatory requirements while enhancing safety through reduced fuel system contamination risk, ultimately lowering overall NGS program costs. Best of all, Pall’s partnerships with OEMs and Satair provide a continuous air quality MRO solution that carriers can depend on, a definite boon to efficiency, safety, and profitability.

Pall Partnerships


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