Manufacturers are investing in research to make aircraft quieter ("Sound thinking", Flight International, 17-30 December 2002), but this will not stem today's tide of complaints from airport communities: "radical thinking" is not just needed "beyond 2020".

Chapter 4 standards were agreed on the basis of current production, rather than any prospective gains in noise performance. The International Civil Aviation Organisation has traditionally adopted a conservative approach where the rule of thumb for deciding the technical feasibility of a new standard is that manufacturers can already meet it with their existing products. Since Chapter 3 was introduced from 1977, ICAO has been unwilling to use standards to drive noise technology. Almost 30 years will have elapsed between Chapters 3 and 4 coming into force.

Based on their performance against Chapter 3, the overwhelming majority of aircraft delivered since 1995 already meet Chapter 4. Without further action, major European airports may already have seen most of the benefits from Chapter 4, an uncomfortable conclusion for regulators reaching decisions on the new chapter. Even a future step change in technology may have only limited impact on the noise climate if: (1) fleets turn over slowly as aircraft remain in revenue service for 30-35 years; and (2) there is further growth in traffic. Improvements might come faster if new technology could be retrofitted.

Future developments, promising as they may be, will not address today's challenges. They may have to battle with the effects of traffic growth implied by forecasts used by ICAO's Committee on Aviation Environmental Protection. Piecemeal operational restrictions at individual airports may go some way to reduce pressures from particular local communities, but implementation has to negotiate ICAO's balanced approach. More radical action may be needed. The approach adopted to retire noisier Chapter 2 aircraft is hardly likely to find more favour in today's tough economic climate for airlines. A change of policy to use standards to drive change may be equally unpopular. But what will be the costs of inaction by ICAO faced with such difficult choices?

Martin Wright Sutton, Surrey, UK

Source: Flight International