Terminal 5 design incompetences - where do I begin ?
I'll just discuss one aspect of the master design, which the architects were responsible for - the architects who won all those design awards for the building (don't be misled by this, by the way - in the architecture profession all the awards for new buildings are lined up among the cognoscenti long before the building is even opened).
Arriving passengers into the remote pier, all heading for the central terminal. Everyone gets off the aircraft. Firstly there is an escalator down. Now escalators are fine for moderate, steady flows, not occasional high capacity rushes like all passengers out of a 747. So there's a big pile up at the top of the escalator to get on it.
Down and down into the basement, and onto the shuttle train. By now the moderate, steady stream is coming down, and all wait for the train, which is a high-capacity, intermittent frequency form of transport, so everyone gets in quickly, then the doors close in the face of those continuing to come down (notably those on short connections it seems), and we are off on a trip which is ludicrously short for a shuttle train's cost of installation, for a range of reasons.
A few seconds later, at the main terminal, all the train doors open and everyone can get out together - to be faced with another set of escalators upwards, and the same crowding problem as when disembarking the aircraft.
So, we have arrived at a high level in the building, are then taken to the bottom level, and almost immediately afterwards transported upwards again, with multiple disruptions to passenger flow along the short way.
Honestly, any first year architectural student would be laughed out of the lecture room by the Professor for such an arrangement.