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What happens to the long range cruise speed when descending below the optimum altitude for a jet aeroplane?
  • A
    Mach number decreases.
  • B
    Mach number increases.
  • C
    Mach number remains constant.
  • D
    EAS increases.

Refer to figure.

Long-Range Cruise (LRC) speed is the traditional cruise speed. It has been historically defined as the speed above Maximum-Range Cruise (MRC) speed with a 1 percent decrease in fuel mileage, but a 3-5% gain in cruise velocity.

It is derived as an EAS from the total drag curve at 1.37 VMD.

  • Take a look at the attached graph, if "E" is kept constant, Mach number for LRC increases as altitude increases. Likewise, it will decrease with decreasing altitude.

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