Velocity Maximum Range Cruise (Vmrc) is the speed that gives the maximum possible still air range for a given fuel load. A description of what is required to achieve maximum range can be found in the string "for those in the know" in this forum. Vmrc is obtained by setting a Cost Index of Zero in the FMC.
Although flying at Vmrc gives the lowest fuel cost for any given distance (in still air) it does not take into account factors such as non-fuel costs and what trip duration might get you the most passengers. If fuel is cheap, non-fuel costs high or if it possible to achieve a large increase in passengers by reducing trip time, it would be better to fly at a higher speed. This will increase fuel costs and reduce range, but might produce a more profitable deal overall. This is achieved by setting a Cost Index greater than zero.
Velocity Long Range Cruise Vlrc is about 5% faster than Vmrc but uses only about 1% more fuel. So trip time is reduced by 5% but you burn a little more fuel.
Last edited by Keith.Williams.; 17th Oct 2004 at 22:17.