Blip
This is an eminently sensible precaution now that airborne navigation has become so accurate that radar altimeters will pick up an underflying aircraft. One of NATS' biggest safety concerns is level busts and should one occur during opposite direction airborne navigation at this degree of accuracy there is little between us and disaster. To me this is an example of good airmanship which ought to be encouraged. When on your own navigation, 250metres is absolutely nothing to ATC; anybody who is relying on that 250m for his separation is acting unwisely.
However, so as not encourage a reckless attitude to ATC instructions generally, this is not appropriate or necessary when under ATC vectors. For example, the LTMA approach sectors work to zero tollerance on traffic spacing. Into strong winds we quite often deliberately "erode" radar separations on the base legs so that we can get traffic tightly spaced on final. Applying a tolerance to the heading or speed instructions is not acceptable.
Just last week I had Far Eastern traffic (with a brit voice) reduce from 180kts to 165kts when into wind on base leg at about 12nm from touchdown. (The traffic following him was on the opposing base and had a 30kt tailwind.) The mode S showed me he had reduced and when I asked he said "we have slowed to 165 is that alright?" I said "well no actually, I now have traffic behind you that is too tight." I was forced to take this traffic (and the subsequent) through the centreline to maintain vortex spacing and in concentrating on that priority I was wide on the one behind that. Immediately I noticed this guy's indicated speed come back up to 180 so it is not as if he HAD to slow down for technical reasons.
All the guys I know here are sympathetic to the different speed equirements of the varous types, eg. B757s and BA46s being slow and B773s being fast. We have noticed over the past few years that more and more aircrew are advising us early if they have a particualrly fast or slow Vref and this is to be encouraged; doing your own ATC isn't.
Point 4