Originally Posted by SNAM
C.I. is the relationship between TIME RELATED costs and FUEL RELATED costs and is used by the FMC to calculate, especially using Boeing's "salang", VNAV economy speed. A change to C.I. will effect CLIMB, CRUISE and DESCENT speeds. C.I. zero (0) for example will provide a cruise speed of approximately MAX. RANGE speed (or MRCruise). Conversely, a C.I. of, let's say, 5000 - or more - will provide the thrust limit or the MAX. SPEED from the aircraft's performance.
C.I. is simply an equation i.e. :
C.I. = Cost of Time / Cost of Fuel
For example, a C.I. of zero (0) povides a fuel saving of 1% when compared to Long Range Cruise (LRC) , but will also result in a 3% increase in block time! Conversely, selection of a C.I. of 4000 will yield a 5.5% savings in block time, but at the expense of a 24% increase in block fuel. Some flights may be planned at a fixed Mach number when necessary to meet ATC requirements.
... On short flights, quite often, "time" might be more important then Fuel savings, and/or v.v..
SNAM
Hi, just wondering where the fuel figures you have quoted came from?
Also, could anyone roughly give an indication of what aircraft speeds (ie. Mach) relate to particular Cost Indices? I'm assuming it depends on the cost structure inputted by the airline but a rough stab for something like an A330-200 at cruise alt will do (and would be much appreciated).
CI=zero => Mach?
CI=500 => Mach?
CI=999 => Mach?
Apologies If I've asked the wrong kind of question. I'm new and I'm sorry to admit that I'm an engineer, not a pilot!
Cheers,