Light Weight / Long Roll
 

Took a short haul (<1000 miles) flight from Heathrow the other night in a 767. Load was probably 60 or less, they had to retrim the plane as a result. I was expecting to leave the surly bonds of earth in a single bound, but the engines did not appear to be really trying and the take off roll appeared to be much longer than usual.
Is this just to save fuel or is there another reason? Just curious.

Airlines use a 'derate' system to reduce engine wear. It is called 'reduced thrust' or 'assumed temperature' in Boeings and 'flex' in that strange French thing:)

It means using far less thrust than full power when weight/runway length allow. Try a PPRune 'Search' for some of those terms.