frequentflyer2 - I'm not a pilot but an ex-City ATCO so I'll explain as best I can remember.
BCA agreed with the planning authorities many years ago that they would endeavour to achieve a bias of flights arriving and departing over Belfast Lough to try and minimise the impact on local residents. We always tried to achieve the magic figure of 70% which we did most months with some way above that. To that end, we had an agreement with based airlines that they would accept up to a 10kt tail wind for runway 04 deps and 22 arrivals subject to their operational considerations for each flight. As 99.9% of flights went eastbound to some degree, most crews happily accepted 04 for deps.
However, when you're playing both ends against each other, it can get a bit close and since there is no noise abatement procedure off 04 when turning left (due to the Harbour Estate not having any residents), we were able to utilise the 'left turn through the overhead on track Ringa/Duffy etc' procedure. Not a published procedure, but then again, not against any rules. It expedited deps and didn't hurt anyone. Another dep you might see is left off 04 towards the north Loughshore then parallel the final approach (we used to do this for the Scottish bound ATPs) rather than take them south then north.
Anyway, many of us lived in North Down (Bangor mainly) and couldn't be doing with noisy planey things over our houses, by jiminy no!