Originally Posted by
Captain Schmidt
Have never noticed it on any of the US airlines - they are just plain old "United 918", "American 101" etc. And I also noted that it wasn't all the BA flights, just some.
Actually, United uses this frequently, though not necessarily for the same reason as other airlines or countries.
United has some routes with a single flight number but a change in aircraft. For example, United 900 is LAX-SFO, then a different plane flies SFO-FRA. If the first flight is delayed, they could both be in the air at the same time, so ATC will call one "United 900 Charlie" or "United 900 Tango" or whatever.