Reference:R&D Report 9823 Title:Assessment of Revised Heathrow Early Mornings Approach Procedures Trial Description:This report describes a study (using primarily the Heathrow Noise and Track-Keeping (NTK) system) to assess the changes in aircraft operation and noise impact arising from a trial revision of Heathrow early mornings landings procedures, which was initiated in September 1995 for westerly approaches. The study found that there was a high degree of compliance with the trial procedure, and that overall the environmental benefits were positive. Between 0400 and 0600, there was a reduction in noise exposure in the area between 9 nm and 17 nm from touchdown of up to 1.5 dBA SEL, as a direct result of the revised procedure. Some additional noise increases and reductions, of up to about 2 dBA SEL, were caused by ground track changes, resulting from the tendency for aircraft to join the localizer further out under the trial procedure; the increases occurred in small localised areas and from very low base levels.
The opportunity was taken to consider whether the trial might have affected the rate of achievement of Continuous Descent Approaches (CDA), which influences noise at greater distances from the airport. None was observed; moreover there appeared to be little change since CDA was first implemented in the 1970s. Additionally, two quite separate trials of night-time runway alternation took place during the period of the early morning procedures trial; the alternation pattern did not appear to have had a significant impact on vertical profiles, but it produced marked changes of noise exposure due to displacement of some approach paths from runway 27L to 27R.