Originally Posted by
Asturias56
At places like LHR you can see the 4 aircraft at east in a nice line for landing - that's 12-15 miles. But as FD says that's more to corall the traffic into the system than any ILS driven constraint
It's also for noise considerations, making arrival flightpaths more predictable. The Heathrow AIP requires that aircraft be stabilised on the ILS by 2500' (roughly 8 nm from the runway) in daytime and 3000' (10 nm) at night.