An overwing slide deployment does not involve a door SFAIK. If the aircraft is pressurised a door cannot be opened as it comes inboard and this cannot be done against the internal pressure. The overwing slides are stowed in the top, inboard surface of each wing. www.youtube.com/watch?v=tIFCPUGBNWM
It was really noisy this morning as it was quite low. It drowned out the radio.
At first I thought it was one of the big helicopters that we get down this way sometimes (a flight of Merlins went past a couple of months back) or a rescue helicopter dropping of at the local A&E which is just up the road from me.