Compare block times on a route such as LHR - CDG now with thirty years ago. A 15 min increase is not unusual (mostly longer taxi times, also some extra holding). I couple of years ago I travelled from JFK to Washington DCA with a timetabled block time three times the flight time and double that Eastern were advertising for their LGA - DCA Shuttle in the seventies. Taxi times at JFK around 1700 are rediculous. Mind you, the airline had an impressive on time arrival record.
In regard to flight rather than block time, I'm not a pilot so I'll leave the detailed discussion to the experts, but deviating from optimum cruising speed costs money. I was delayed a couple of hours returning to LHR from HKG a couple of years back after a fault cropped up whilst we were taxiing. The captain said that things had changed and he hoped to shave up to thirty minutes off the flying time. I presume he topped up on fuel before the second push back.
Nothing to do with aviation, but many shipping lines are saving fuel by super slow cruising. Reducing the speed of a container ship by 20% may reduce fuel burn by 50%. I don't know what the trade off is for a typical aircraft - help from experts required - sadly there is not much you can do in a hold. Substituting a prop for a jet will can save you a lot of fuel.
Last edited by Peter47; 15th Dec 2012 at 09:47.
Reason: Grammar etc