But a colleague assured me that I was mistaken and that all aircraft overflying Sheen are already aligned with the southern runway.
He is correct. You are mistaken.
They both stated that planes landing at Heathrow were aligned with the runway centerline when they passed over Sheen.
They are correct. Aircraft are required to join the ILS at or above 2500 feet (3000 feet at night). That means that they must be on the runway centreline by around 8nm from the runway during the daytime - roughly by the time they are over Putney.
But Heathrow’s recent ‘noise respite trial’ surely depends on the ability to direct incoming flights around the two noise relief zones terminating in neighbouring Putney?
The "no-fly" zones made little or no difference to the flightpaths of aircraft by the time they had reached Putney.
Does Heathrow’s set a specific ILS azimuth approach for incoming flights?
If you mean "is the ILS offset from the centreline of the runway?", the answer is No.
I reckon a couple of pints at the Hare and Hounds are resting on the answer – but who will be buying?
Looks like the drinks are on you.