As far as I know, airports try to setup the operations to have planes descend over cities, and climb away from them, to minimize noise. Sometimes this is not po

As far as I know, airports try to setup the operations to have planes descend over cities, and climb away from them, to minimize noise. Sometimes this is not possible because of winds, so there will be a reversal. Sometimes it's not possible to avoid climbing over cities because the city ended up engulfing the airport (e.g. Heathrow) - so they will alternate directions to give various towns a break.