This from
'The Going Down Bit'. It relates to the B757 and was written several years ago so might have been superseded by new techniques.
<<OH NO . . . WE’RE ABOVE THE GLIDESLOPE!
Busy airport - single runway – ATC doing their best to get flights in and out without holding anyone up. The radar controller’s vectors might turn you onto the localiser while you’re still above the glideslope. No problem: get some more drag out. But suppose you then capture your last cleared altitude before you get onto the glide. An ALT CAP is the last thing you need at that point. Here’s a solution: once you have captured the LOC and if you are absolutely sure you’re above the genuine glideslope (by cross-checking range information), arm GS and set the MCP altitude window to final fix altitude. Stay in FL CH (check that speed window!) and use whatever drag is necessary to capture the GS. Remember that the task will be more difficult if you’ve got the TAI on. If you’re not established on the GS by the time you arrive at the final fix, start thinking about a go-around, especially if you are IMC.>>