According to Swiss aviation law (SR 748.0, LFG Art. 58), emissions from all engine powered aircraft have to be evaluated and tested. The legal requirement also incorporates aircraft engines that are currently unregulated and do not have an ICAO (International Civil Aviation Organization) emission certification – like piston, helicopter, turboprop and small jet engines. Emissions data are necessary for emission and immission inventory purposes as well as for issues directly related to environmental protection.
Today, there are only few emissions data available for aircraft piston engines. Therefore, Swiss FOCA (Federal Office of Civil Aviation) started with in-flight emission measurements of piston engine powered aircraft.
First results showed that the still predominant "old technology" aircraft piston engines developed in the 50ies and 60ies can produce CO and HC emissions in the magnitude of modern standard airliners during landing and take-off, although the fuel consumption is not significant compared to airliners. Manual air-fuel mixture control during flight, commonly used for aircraft piston engines, adds a particular degree of complexity to emission measurements and with portable emission measurement systems, it was possible to properly investigate real world emissions performance.
As a result of successful in-flight emission tests, a standardized ground measurement methodology has been developed. Emissions data of a variety of aircraft piston engines are now openly available.