Why 270 knots will not work:
London Terminal and Approach controllers are the world's finest. In the UK IFR operation they achieve a 98% landing rate efficiency at Heathrow over prolonged periods. HOW? Well they need a ready and available supply [or reservoir] of the correct mix of aircraft types to stream and sequence for best results. This is realised by the "full stack" principle which translates into absolutely no wasted space. If aircraft are streaming slowly towards the stack there will be an inevitable reduction in efficiency and I suspect there will need to be a 5% reduction in landing slots during peak demand.
THE CON: this is being "sold" to the airlines on the premise that the long 270 knot econ descent will result in minimum stack holding......in fact the gains can only be short term for the leading aircraft....eventually the stacks will still fill up but the aircraft will have burnt more gas at lower levels before they get there due to the flatter profile. Remember that hundreds of flights will still converge on London from all points of the planet, and they are catching up at a higher closure rate than pre-trial.
On the Area side these aircraft will be in my sector for longer and will be less "controllable". I expect the sector capacity to be modified accordingly...any bets on that?
Regards 055....[NATS third most experienced operational controller]