Skytrain10,
You mention that Heathrow "at last has a mini viewing deck north of the airport" ?????? As far as I know all Heathrow has in terms of viewing areas is the Heathrow Academy, and other undesignated areas around the airport where spotters gather. There are no viewing decks around Heathrow from where you can watch the planes, unless your airside of course. I wish there was one though!