Graham Warwick/WASHINGTON DC

A modified plan to reduce harmful aero engine emissions has been recommended by the International Civil Aviation Organisation (ICAO).

ICAO's Committee of Aviation Environmental Protection (CAEP) has approved a plan which would cut emissions of nitrogen oxides (NOx) while encouraging development of more fuel-efficient engines producing less carbon dioxide (CO2).

The 1995 meeting of the CAEP had rejected calls to reduce NOx emissions by 16%, as it would be impossible to develop engines with high enough pressure ratios.

Howard Aylesworth, of the US Aerospace Industries Association, explains that increasing the pressure ratio is desirable in attempting to lower fuel consumption and lower CO2 production, but that an inevitable by-product of the higher pressures and temperatures is an increase in NOx emissions.

The revised proposal therefore relaxes the NOx stringency standards for engines with pressure ratios of 30 to 62.5 -Aylesworth says that the highest ratio achieved to date is in the low 40s.

Meeting in Montreal in early April, the CAEP also approved a fleet protection proposal to only apply the new NOx rules to new engines certificated from 2004 onwards, while it urged faster progress on air traffic modernisation, which it estimates could reduce emissions by 6-17%.

Conventional wisdom holds that aviation accounts for 2-5% of greenhouse gas production, although a recent study by the Intergovernmental Panel on Climate Change puts the contribution from aircraft emissions at closer to 10% once the ozone created in the troposphere is taken into account.

The protocol signed by the international community at the Kyoto summit in December excludes aircraft emissions, but the CAEP plans a proposal for its next meeting, tentatively scheduled for February 2001, on how aviation should contribute to agreed limits.

Source: Flight International