At any time that ANY aircraft conducts a climb at less than, or more than, optimum range climb speed you will consume more fuel. This speed is typically slightly higher than best Rate of climb speed, and significantly higher than the best gradient speed.
The best Rate of climb can be refined further to optimize time and fuel. Remembering that up to 20 to 30 Knots off optimum will have only minimal effect upon excess power. An econ climb speed a little above best rate will have a negligible effect upon rate of climb, but put the aircraft 30 miles or so further down track at top of climb. The very slight increase in climb time and fuel is more than off-set by the extra distance covered in the ‘fuel expensive’ climb, and elimination of the incremental cruise.
Operation cost equations vary from organizations but are most always benefited by a time reductions. Low cost indices in many cases are opted for based purely on face value of misinformed accountancy rather than laws of physics and cost factors.
Last edited by jimmyg; 5th Sep 2012 at 04:52.