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A good understanding of cruise flight can not only help crews operate efficiently and save their companies money, but can also help them deal with low fuel situations. As an additional benefit, the less fuel consumed, the more environmentally friendly the flight.
CRUISE FLIGHT IS THE PHASE OF FLIGHT BETWEEN CLIMB AND DESCENT. by William Roberson, Senior Safety Pilot, Flight Operations;
Robert Root, Flight Operations Engineering; and
Dell Adams, Flight Operations Engineer

This article is the second in a series exploring fuel conservation strategies.

This article defines cruise flight, presents various cruise schemes, and outlines the effects of wind on cruise speed calculations. It also discusses the relationship between cruise flight and cost index (CI) which was discussed in the first article in this series, "Fuel Conservation Strategies: Cost Index Explained" in the second-quarter 2007 AERO.

Used appropriately, the CI feature of the flight management computer (FMC) can help airlines significantly reduce operating costs. However, many operators don't take full advantage of this powerful tool.


Cruise flight is the phase of flight that falls between climb and descent. The largest percentages of trip time and trip fuel are consumed typically in this phase of flight. As an aside, unanticipated low altitude maneuvering, which also impacts trip time and fuel significantly, can often be avoided through appropriate cruise planning.

The variables that affect the total time and fuel burn are speed selection, altitude selection, and, to some degree, center of gravity (CG). This article focuses on speed selection.

A number of high-level objectives may influence speed selection. These objectives, which depend on the perspective of the pilot, dispatcher, perfor­mance engineer, or operations planner, can be grouped into five categories:
  1. Maximize the distance traveled for a given amount of fuel (i.e., maximum range).
  2. Minimize the fuel used for a given distance covered (i.e., minimum trip fuel).
  3. Minimize total trip time (i.e., minimum time).
  4. Minimize total operating cost for the trip (i.e., minimum cost, or economy [ECON] speed).
  5. Maintain the flight schedule.

The first two objectives are essentially the same because in both cases the airplane will be flown to achieve optimum fuel mileage.

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