Source : IATA
Efforts to perform realistic cost index calculations in specific, airline-relevant cost brackets (low, medium, high) should pay off, rather than over-meticulous but undocumented computations of time-related to fuel-related cost ratios. The practical case for this is made in the next section.

2.4 Variation of airline practices
A large variation exists in how airlines actually use the cost index : some of this variation is related to specific operator requirements, some of it may reflect difficulties with the concept that may lead to inappropriate application. Some cases are cited here :
Airline A : use of the cost index to approximate Long Range Cruise (LRC)
Airline B : use of the cost index between LRC and Maximum Range Cruise (MRC)
Airline C : higher  cost  index  if  necessary  for  scheduling  irrespective  of  fuel 
consumption  issues 
Airline D : Cost  index  variation  according  to  fuel  prices  irrespective  of  time 

considerations (transparent / not considered) Airline E : use of the cost index to approximate LRC, except cost index = 0 for fuel
critical routes Airline F : cost index calculation resulting in cruise speed between MRC and LRC Airline G : cost index calculation resulting in cruise speed slightly below LRC
Airline H :  use of the cost index to meet schedule requirements route by route Airline I : use of the cost index route by route differentiating by fuel price only Airline J : adoption of cost index values by adapting from other aircraft models/ manufacturers Airline K : adoption of cost index values by a adapting for speed requirements only Airline L : cost index adaptation according to sector fuel price variations after an initial rigorous fuel and time calculation.

3. COST INDEX TABLES
Although we recommend treating each airline route individually, cost brackets ranging from low to medium to high fuel and time-related costs led us to consider the following cost index tables.

3.1 A300/A310 Family
Considering, with good approximation, that the following range of time-related costs cover the maintenance cost difference between A300 and A310 as well as the cabin crew contingent (plus or minus two) difference, the following cost brackets result :
6 < Hourly maintenance cost < 12 (US$/min)
+ 7 < Crew cost < 14 (US$/min)
13 < Time-related cost < 26 (US$/min) NB : Crew composition = 2 cockpit crews + 8 (± 2) cabin crews. In turn, the following cost index tables reflect these cost ranges for the A300 and for the A310.
Table 1. A300/A310 cost index
(kg/min) (Honeywell FMS)
TIME COST (US$/min) FUEL COST (US$/USG)  LOW < 15  MEDIUM 15 < to < 20  HIGH > 20 
LOW < 0.7  65  85  100 
　
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