Yes, BA is non-Schengen, so no immigrations or security (as you are arriving from the US). The vast majority of BA LHR flights depart from a D-gate in the southern fork (i.e. far end) of the concourse. FlyBe operated flights may get a D6 bus gate. If your incoming flight is pretty much on time you will be fine. If not, your fallback plan will of course mean that you have to enter Schengen at AMS and go through passport control.
Johan