Cost index is derived from the following formula, ocph/(fp*100)
opch= operating cost per hour, (US$ per hour)
fp= fuel price, (US$ per kg)
The operating costs per hour has a multitude of factors which ifluence it, turn around times, airframe life, crew costs, delayed flight, and MAINTENANCE COSTS. Think of a operting cost and add it to the
variable "operating costs".
Maintenance costs are the least known about of all the variables by the Bean counters.
However, the price of fuel is the biggest influence in determining the cost index