On the Benefits of Lower Mach Number Aircraft Cruise


The Aeronautical Journal book cover

A Filippone
The Aeronautical Journal
Aug 2007

The paper reviews the issue of cruise Mach number and addresses the benefits of operating subsonic commercial aircraft at speeds below the long-range cruise speed. The case considered is the flight of transport aircraft for flight segments up to 1,000 n-miles. It is shown that the fuel burned is decreased by as much as 1.8% on a nominal 1,000 n-mile stage length for operation around the long-range cruise Mach number, or below. This is achieved at a cost of a marginal delay on each flight segment (less than 3 minutes). The longer flight time is likely not to affect the daily operation of the aircraft. The fuel saving is compounded, because the Gross Take-Off Weight (GTOW) is recalculated to take into account the reduced fuel consumption at each flight segment. The analysis into the environmental benefits includes the reduction in , and emissions, and the heat released in the high atmosphere. Sensitivity analyses are carried out on the take-off weight, on the aerodynamic coefficients, on the transonic drag rise and the weight uncertainty. It is predicted that the optimal operation of the example aircraft over a nominal 1,000 n-mile route can reduce the fuel consumption by as much as 150,000 kg per year in comparison with an operation at the long-range Mach number. The aircraft model has a maximum take-off weight of 170,000 kg and is powered by two GE CF6-80C2 engines.