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ICAO booklet: Annex 16 to the Convention on International Civil Aviation Environmental Protection

The following is the text of an ICAO booklet that outlines the history and purpose of the international standards for aircraft noise in the vicinity of airports (Volume 1) and also the standards for aircraft engine emissions (Volume 2). ICAO's 229 page ANNEX 16 Volume 1 is available in the Fly Safe sub-domain, it includes all amendments to 2000.

Annex 16 (Volumes I and II) deals with the protection of the environment from the effect of aircraft noise and aircraft engine emissions - two topics hardly thought about when the Chicago Convention was signed. Aircraft noise was already of concern during the formative years of ICAO, but it was then limited to the noise caused by propellers whose tips rotated at speeds approaching that of sound. This concern increased with the introduction of the first generation jet aeroplanes in the early 1960s and accelerated with the growth in the number of jet aircraft in international operations.

Aircraft noise is a function, among other things, of the power of the engines that propel aeroplanes through the atmosphere. Reduce the power and you reduce noise, but at the same time you may affect the safety characteristics of the jet aircraft.

In 1968, the ICAO Assembly adopted a resolution which conceded the seriousness of noise in the vicinity of airports, and instructed the ICAO Council to establish international specifications and associated guidance material to control aircraft noise. In 1971, the Assembly adopted another resolution recognizing the adverse environmental impact that may be related to aircraft activity. This resolution placed on ICAO the responsibility to guide the development of international civil aviation in such a manner as to benefit the people of the world and to achieve maximum compatibility between the safe and orderly development of civil aviation and the quality of the human environment.

Annex 16 dealing with various aspects of aircraft noise problems was adopted in 1971 on the basis of recommendations of the 1969 Special Meeting on Aircraft Noise in the Vicinity of Aerodromes. These aspects included: procedures for describing and measuring aircraft noise; human tolerance to aircraft noise; aircraft noise certification; criteria for establishment of aircraft noise abatement procedures; land use control; and ground run-up noise abatement procedures.

Shortly after this meeting, the Committee on Aircraft Noise (CAN) was established to assist ICAO in the development of noise certification requirements for different classes of aircraft.

The first meeting of this committee developed the first amendment to Annex 16, which became applicable in 1973 and included noise certification of future production and derived versions of subsonic jet aeroplanes. During subsequent meetings, the Committee on Aircraft Noise developed noise certification standards for future subsonic jet aeroplanes and propeller-driven aeroplanes, and for future production of existing supersonic transport aeroplane types and helicopters. It also developed guidelines for noise certification of future supersonic and propellerdriven STOL (short take-off and landing) aeroplanes as well as installed APUs (auxiliary power-units) and associated aircraft systems when operating on the ground.

A resolution adopted by the ICAO Assembly in 1971 led to specific action on the question of engine emissions and detailed proposals for ICAO Standards for the control of engine emissions from certain types of aircraft engines. The Committee on Aircraft Engine Emissions (CAEE) was subsequently established with a view to develop specific Standards for aircraft engine emissions.

These Standards, adopted in 1981, set limits for the emission of smoke and certain gaseous pollutants for large turbo-jet and turbofan engines to be produced in the future; they also prohibit the venting of raw fuels. The scope of the existing Annex 16 was widened to include engine emission provisions and the document was retitled Environmental Protection.

Volume I of the reorganized Annex 16 contains provisions related to aircraft noise while Volume II contains provisions related to aircraft engine emissions.

In Volume I, different aircraft classifications form the basis of noise certification. These classifications include subsonic jet aeroplanes for which application for the certification of the prototype was accepted before 6 October 1977; for those accepted on or after that date; for propeller-driven aeroplanes over 5 700 kg; for those not exceeding this mass; for supersonic aeroplanes for which application for certification of the prototype was accepted before 1 January 1975; and for helicopters for which the application for certification of the prototype was accepted on or after 1 January 1980.

For each classification of aircraft type, a noise evaluation measure has been standardized. Except for propeller-driven aeroplanes not exceeding 5 700 kg maximum certificated take-off mass, the noise evaluation measure is the effective perceived noise level, expressed in EPNdB. The EPNdB is a single number indicator of the subjective effects of aircraft noise on people, taking into account the instantaneous perceived noise level and duration.

Various measurement points, maximum noise levels at lateral, approach and flyover noise measurement points, along with flight test procedures, have been designated for these types of aircraft.

Noise certification is granted by the State of Registry of an aircraft on the basis of satisfactory evidence that the aircraft complies with the requirements which are at least equal to the applicable Standards set out in this Annex.

In Volume II of Annex 16, there are Standards which prohibit the intentional venting of raw fuel to the atmosphere from all turbine engine powered aircraft manufactured after 18 February 1982.

There are also Standards which limit the emission of smoke from turbo-jet and turbofan engines intended for propulsion at subsonic speeds and manufactured after 1 January 1983. For engines intended for supersonic propulsion, similar limitations apply to engines manufactured after 18 February 1982.

Also included are Standards which limit the emission of carbon monoxide, unburned hydrocarbons and oxides of nitrogen from large turbo-jet and turbofan engines intended for subsonic propulsion and manufactured after 1 January 1986. These Standards are based on an aircraft's landing and take-off (LTO) cycle. In addition to these Standards, Volume II contains detailed measurement procedures and instrument specifications and details the statistical methods to be used in assessing test results.

In 1983, the CAN and CAEE committees were amalgamated to form the Committee on Aviation Environment Protection (CAEP), as a Technical Committee of the ICAO Council. Since its establishment, CAEP has further developed the Standards in Annex 16 for both aircraft noise and aircraft engine emissions.

Concerning aircraft noise, on the basis of recommendations by CAEP, the Council of ICAO in 2001 adopted a new Chapter 4 noise standard, more stringent than that contained in Chapter 3. Commencing on 1 January 2006, the new standard will apply to newly certificated aeroplanes and to Chapter 3 aeroplanes for which re-certification to Chapter 4 is requested.

This new Standard was adopted at about the same time as the ICAO Assembly endorsed the concept of a 'balanced approach to noise management' developed by CAEP that is comprised of four elements, namely reduction of noise at source, land-use planning, operational measures, and operation restrictions. For further details, see the Consolidated statement of continuing ICAO policies and practices related to environmental protection.

Concerning aircraft engine emissions, there has been a change in the focus of the Organization's work. While it was initially based on concerns regarding air quality in the vicinity of airports, in the 1990s it was expanded to include global atmospheric problems to which aircraft engine emissions contribute, such as climate change. As a result, consideration is being given to further development of the ICAO emissions Standards to take account of emissions not only in the LTO cycle, but also during the cruise phase of operations.

In both 1993 and 1999, on the basis of CAEP recommendations, the Council of ICAO adopted more stringent Standards defining the emission limits for oxides of nitrogen. At the time of writing, a third revision of these limits was under consideration by the Council.

Environmental protection has become one of the biggest challenges to civil aviation in the twenty-first century. Since it was first adopted, Annex 16 has been further developed to meet new environmental concerns and to accommodate new technology. The Organization will continue to keep the Annex under review, consistent with its aim of achieving maximum compatibility between the safe and orderly development of civil aviation and the quality of the environment.