Originally Posted by
DaveReidUK
It's not unknown for a flight with an STA post-0600 to land before that time, probably a couple per day on average.
Lists of permitted pre-0600 arrivals get exchanged between Heathrow, the tower and Swanwick to ensure only those who are permitted to land before 0600 do so, according to the night quota system.
Usually if a post-0600 arrival is permitted to land before 0600, it’s because it’s been swapped with a pre-0600 arrival that is running late that day.