In 1999 the runway alternation scheme was extended to the night period and – at night only – for easterly operations.

There is a weekly rotation of westerly and easterly arrivals after the last departure until 06:00, subject to weather conditions on any particular night. 

This has resulted in a more even split between westerly and easterly operations than the previous figure of nearly 90% of early morning arrivals overflying  London in an average year at Heathrow.