Re: F4 Phantom - Flying Bus???
At the risk of being called a spotter, and wearing my shabbiest anorak, here we go. Yes, the Spey-engined FGR2 could use both 7th and 12th stage air for boundary layer control. However, if I recall correctly, the on-speed was only 3 kts slower using both, and it casued the TGT to rise a few degrees thus adding wear and tear on the engines. So, a Bleed Control Switch was used in the Isolate position to select 7th stage air only. I'm a little hazy here in that it could have been 12th stage only, but I think I'm right in saying 7th.
Ground school on the F4 was a very long time ago, and I haven't flown one since about 1986, so forgive this humble contributor if I've got it all round my neck, as they say in Lincolnshire.
Still a great jet, though!