Originally Posted by Mofomat
The C class seating on the B767 AMS-LHR-AMS flights is exactly the same as used on the long haul routes. They use this a/c on the AMS-LHR route to increase fleet utilisation, rather than having the a/c sat on the ground at Schiphol in between long haul runs.
That's part of it. The other issue is that LHR is slot-controlled, which means extra flights have to be approved, so the only easy way to increase the amount of available seats is to upgrade existing flights to bigger aircraft.
That's why LH flies A300s to LHR from FRA, for example, or why you see lots of A321s from a variety of airlines there.