SAE adopts recommended practice on bleed air purity

  • 30-Jun-2008 07:16 EDT
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ARP4418 provides guidance to measure contaminant levels in engine bleed air used in aircraft environmental control systems. This photo from Honeywell shows an engine being tested for bleed air purity at the company’s remote testing facility near Phoenix.

SAE International has adopted ARP4418A, an aerospace recommended practice that provides guidance to measure contaminant levels in engine bleed air used in aircraft environmental control systems.

It is necessary to have a document such as ARP4418A to assist companies in showing compliance to applicable national and international regulations (FAA 14CFR Part 25.831 and EASA CS-25.831) when they are certifying breathing-air supplies from aircraft engines and auxiliary power units, said Richard Fox, the sponsor of ARP4418 who works as Staff Scientist for Honeywell Advanced Technology. The recommended practice makes a connection to the recognized European industry standard, PrEN4618, and the NIOSH (U.S. National Institute for Occupational Safety and Health) standard for total particulates, and their recommended allowable limits.

Fox noted that the FAA and EASA have been working to harmonize their various regulations so that manufacturers need not perform different certification tests to demonstrate compliance to, in the case of ARP4418A, aircraft interior air quality. PrEN4618 and NIOSH standards provide the measurable limits that are used to determine compliance, and ARP4418A provides the recommended methods to demonstrate compliance.

This and a number of other standards, guidelines, and recommended practices could potentially help airlines and airframe manufacturers operate greener aircraft, said Fox. These documents provide a full suite of tools to help the aerospace designer build systems that use technology to meet performance-based standards.

The European Union’s standardization body, AECMA-STAN (European Association of Aerospace Industries-STAN) issued PrEN4618-Aircraft Internal Air Quality Standards, Criteria and Determination Methods in 2004. The standard provides recommended limits for marker compounds in aircraft cabin air to ensure comfort, health, and safety.

SAE has published related standards and information reports. AIR4766-Air Quality for Commercial Aircraft Cabins provides the designer with a compilation of information and references on measured values of contaminants within aircraft in normal operation and compares these levels with those of other public areas. In addition, it provides other information so that potential sources of contamination in aircraft can be localized. Recommended practices for design of systems for particulate and gaseous compound removal are found in AIR4766/1-Air Quality for Commercial Aircraft Cabins-Particulate Contaminants and AIR4766/2-Airborne Chemicals in Aircraft Cabins. AIR1796-Engine Bleed Air Systems for Aircraft and AIR1539-Environmental Control System Contamination provide additional information related to environmental systems and contamination control.

ARP4418A-Procedure for Sampling and Measurement of Engine & APU Generated Contaminants in Bleed Air Supplies from Aircraft Engines Under Normal Operating Conditions provides methodology to demonstrate compliance for environmental control systems as mandated by 14CFR25.831. The methodology is based on determining levels of marker compounds referenced in PrEN4618. ARP147-Environmental Control System Terminology provides users new to the area of environmental control systems a document that describes and defines the large number of terms used in the ECS area.

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