This Aerospace Recommended Practice (ARP) describes the continuous sampling and analysis of gaseous emissions from aircraft gas turbine engines. The measured gas species include carbon monoxide (CO), carbon dioxide (CO₂), nitric oxide (NO), nitrogen dioxide (NO₂), total hydrocarbons (CHα where"α" is the hydrogen to carbon ratio of the fuel) and water vapor (H₂O). This ARP excludes engine operating procedures and test modes, and is not intended for in-flight testing, nor does it apply to engines operating in the afterburning mode.
It is recognized that there will probably be major advances in the gas analysis measurement technology. It is not the intent of this ARP to exclude other analysis techniques, but to form the basis of the minimum amount of conventional instruments (those in common industry usage over the last fifteen years) required for the analysis of aircraft engine exhaust. It is the responsibility of the analyst to demonstrate the alternative measurement technology has comparable (or better) performance, than the techniques described in this ARP.
The measurement of other exhaust gas species is beyond the scope of this ARP.
It should be noted the measurement of oxygen (O₂) is generally accepted as essential for assessing data quality, but is not covered by this ARP. Sulfur dioxide (SO₂) is normally not measured using conventional systems but is calculated from fuel sulfur content. Again this is not covered by this ARP.
This ARP has been updated from earlier versions to more accurately reflect the best common practices employed in modern aircraft engine gaseous exhaust emissions testing. This ARP permits the use of alternative instrumentation and a gas divider type instrument to determine the linearity properties of measurement devices. High purity nitrogen is recommended for both span diluent and zero gas on infra-red and chemiluminescence analyzers, such that corrections do not have to be applied to these instruments zero and span readings. Instrument linearity requirements and span gas tolerances have been made more stringent from earlier versions of this ARP, reflecting the improved accuracy from both modern analyzers and gas suppliers respectively.