The DOCsys formula (for aircraft) has 3 major components. Depreciation + Fuel burn + Maintenance.
Well, this might apply to your DOCsys formula.............
In the real world, it looks more like that.........
Method for Calculating Direct Operating Cost
The following is an estimation method known as DOC+I (Direct operating cost plus interest). This method is based on the work of Liebeck and has been applied by Ross
for wide body commercial aircraft. By definition the DOC+I method takes into account the following operating expenditures; flight & cabin crew cost, airframe maintenance, engine maintenance, landing fees, depreciation, interest, and insurance.
Flight Crew & Cabin Crew
The flight deck and cabin crew cost are all based on Block Hours (BH), which is equivalent to the number of trips per multiplied by the average flight time per trip. For
the flight crew there salary is a function of the maximum takeoff weight of the aircraft as
seen in Equation 1. The flight attendants or cabin crew cost is based on an assumed pay rate of 60 dollars per hour.
(# ) (440 0.532*( /1000) gross Flight Crew = BH × of flight crew × + W (Eq. 1) Cabin Crew = BH ×(#of flight crew)×60 (Eq. 2)
Airframe Maintenance
Cost of airframe maintenance is broken down into three parts; labor, materials, and
burden or the cost of taking the aircraft out of operation.
Airframe Maintenance Labor:
Notice that for both the labor and material cost, are based on a historical curve fit developed by Liebeck and are dependent of the number of trips per year, average trip time and the airframe weight.
Landing Fee
The landing fee is based on the operational empty weight of the aircraft and an average of
landing fees in the United States. They may heavily vary in Europe, with possible
additional fees such as NOX emissions or community noise. However this is not captured in this method.
Depreciation, Interest & Insurance
For all of the following methods the total airframe cost must be known, which can be
found using methods found in Raymer. Notice that all of the following equations are
dependent on gross weight that will be found by your sizing code.
Depreciation (1 residual ) Airframe Cost Airframe Spares Airframe Cost Engine Spares Airframe Cost
For the interest calculation it is ok to set the future value of the aircraft to zero since it is difficult to predict this value, especially at the very early stages of preliminary design. Finally, from all of these the total direct operating cost of a commercial transport can be
found:
DOC = Flight Crew + Cabin Crew + Airframe Maintenance + Engine Maintenance +Depreciation + Insurance + Interest