I think what you are referring to, is an attempt to keep the noise away from certain areas of London on westerlies and again certain areas west of Heathrow on easterlies at night between 0400 and 0600, on a weekly basis.
This method uses the skills of Heathrow Approach Controllers for the benefit of some Londoners and some people living west of Heathrow under the approach paths.
Boxes ared used on the radar, as no fly zones during the times above, but do not affect normal operations from 0600.
Last edited by Over+Out; 28th Nov 2012 at 16:36.