getting to grips with the cost index(10)

First of all, we note that time to climb is only slightly affected by the cost index (less than 1 minute) for the A300 and A310 (whatever the engine) between low and high cost indices.
This time difference is higher, however, for the A330 and especially for the A320 (up to 3 minutes) since both the range of climb CAS and climb Mach are rather larger for these two aircraft.
However, to have a representative comparison of these different climb strategies, we have to include the short cruise segments between the "low cost index TOC" and the "high cost index TOC" (see climb profile graph).
The following Table 7 provides parameters and differences in terms of time and fuel at the same geographical point (corresponding to the furthest TOC) thereby summarizing the array of possible climb laws between CI=0 and high cost indices.
Table 7. Climb to FL 330
Time (min) / Fuel (kg)at farther TOC  Difference between low and high cost index 
Cl = 0  High cost index  Time gain  Fuel increment 
A300-600  18.0  2977  17.8  3004  10 s  30 kg 
A310  19.0  2922  18.2  2965  50 s  40 kg 
A320  27.5  1984  26.1  2080  1 min 30 s  100 kg 
A330  23.0  3927  21.7  4068  1 min 20 s  140 kg 
A340  26.8  5532  26.7  5574  10 s  40 kg 

As a general conclusion, we can say that climbing at low cost index is only worthwhile if time to climb is really essential (FL competition, ATC requirement...) since the difference in terms of costs between low and high cost index climbs is very small.

5.3 A340 practical case
Contrary to the A300, A310, A320 and A330, the A340's cost index is only influential on ECON climb Mach but not on ECON climb IAS; the ECON climb Mach corresponding to the ECON cruise Mach at TOC.
The ECON climb IAS is also a function of take-off weight and inserted FL only :
-
the higher the FL, the lower the speed,

-
the higher the aircraft gross weight, the higher the speed.

As shown in Figure 13 and in Table 8 for managed climb at high cost indices, time to climb may be affected when the first requested FL is rather high (higher than optimum) and especially in hot conditions.

Table 8. Climb to FL 350 according to CI (Load 6)
A340-311 /CFM56-5C2
TOW : 230 tonnes
ISA conditions

COST INDEX (kg/min)  TIME (min)  DISTANCE (nm)  FINAL MACH (MN)  FUEL (kg)  FINAL RATE at TOC (ft/min) 
0 50 80 100 150 200  27.4 28 28.6 29 29.5 30  181 187 192 195 200 205  0.783 0.800 0.808 0.812 0.818 0.823  5200 5300 5400 5450 5530 5620  470 460 440 430 400 360 

- In order to be as close as possible to the minimum time to climb without compromising distance to climb, nor reaching too low a Mach Number, IAS/MACHCLIMB schedules, corresponding to the best rate of climb, were defined asshown in the tables of Appendix 4.
　
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