The phased programme to prepare terminals One through Four for the new, wider, longer, jets will involve ripping out departure lounges and boarding bridges and spacing them farther apart.
Because this will reduce available slots, capacity will initially fall, rising again only after the new Boeing and Airbus planes come in to service early in the next century.
Heathrow was designed to handle a maximum flow of 50 million passengers a year but currently sees 54 million. Terminal Five, which will not need modification, is designed to add capacity for 30 million more. Baggage halls in the old terminals will also have to be redesigned, with experts estimating that the conveyor belts and carousels will need to be half as big again as they are now.
Taxiways parallel to the runways will have to be moved to meet the minimum standard for clearance between planes taking off and queuing on the ground.
Officials at the airport refused to reveal details of the plans, however the Airports Council International estimated the average cost for converting international airports will run to pounds 70m. Heathrow, because of its size, could cost considerably more.
The only London Airport currently equipped to take the new Super Jumbo jets, which will be up to 15 metres wider than the old 747s, is Stansted.Reuse content