Formulation to Estimate DOC
The DOC formulation is presented in this section, based on the AEA ground rules . The formulae compute the component DOC per block hour. To obtain a trip cost, the DOC per block hour is multiplied by the block time. Aircraft performance calculates the block hour and block time for the mission range (see Section 13.5.6). The next section works out the DOC values, continuing with the Bizjet example used thus far.
Normally, the DOC is computed for a fleet of aircraft. The AEA suggests a ten – aircraft fleet with a 14-year lifespan and a residual value of 10% of the total investment; these values can be changed, as shown in the next section. Fuel prices, insurance rates, salaries, and manhour rates vary with time. Engine-maintenance costs depend on the type of engine; here, only the turbofan type is discussed. For other types of power plants, readers may refer to .
Total Investment = (aircraft + engine price) x (1 + spares allowance fraction)
Readers must be sure to obtain the Standard Study Price from the manufacturer. The AEA uses the total investment, which includes the aircraft delivery price, cost of spares, any changes in the order, and other contractual financial obligations. In the example, the aircraft and engine price are taken as the total investment per aircraft.
Outstanding Capital = total capital cost x (1 – purchase down-payment fraction)
Utilization (per block hour per annum in hours/year)
TT. Tf 3,750
Utilization, U = —– — x t
(t + 0.5)
where t = block time for the mission.
For the flight crew, the AEA uses $493 per block hour for a two-crew operation. For the cabin crew, the AEA uses $81 per block hour for each crew member.
• Landing fees = (7■8xMTOtWintons) where t = block time for the mission
• Navigational charges = (°-5xraJeinkm) x умтоуши™ where t = block time for the mission
• Ground-handling charges = (100xPaylotad in tons) where t = block time for the mission
The landing and navigational charges are MTOW-dependent and the groundhandling charges are payload-dependent. In practice, the crew salary is also MTOW – dependent but the AEA has kept it invariant.
• Airframe maintenance, material, and labor
(a) airframe labor
where Wairframe = the MEW less engine weight in tons
R = labor manhour rate of $63 per hour at the 1989 level t = block time for the mission
(b) airframe material cost
where Cairframe = price of aircraft less engine price in millions of dollars
• Engine maintenance, material, and labor
(a) engine labor
0.21 x R x C1 x C3 x (1 + T)0 4
where R = labor manhour rate of $63 per hour at the 1989 level T = sea-level static thrust in tons C = 1.27-0.2 x BPR02 where BPR = bypass ratio
C3 = 0.032 x nc + K where nc = number of compressor stages K = 0.50 for one shaft = 0.57 for two shafts = 0.64 for three shafts
(b) engine material cost
2.56 x (1 + T)0 8 x C1 x (C2 x C3)
where T = sea-level static thrust in tons
C2 = 0.4 x (OAPR/20)13 + 0.4
where OAPR is the overall pressure ratio; C1 and C3 are the same as before.
(c) direct engine maintenance cost (labor + material)
Ne x (engine labor cost + material cost
where Ne = number of engines
block fuel x fuel cost
Table 16.14. Bizjet data for DOC estimation
* 10 passengers
** It has one high-pressure compressor, four-stage low-pressure compressor, and one fan. Aircraft price = $7 million Engine price = $1 million
Total aircraft acquisition cost = $8 million (total investment per aircraft;price includes spares)
Then, DOC per hour = (fixed charges + trip charges)per_hour and DOC per trip = t x (DOC)per_hour and DOC per aircraft mile = DOCx10Q”~t’i°cktime and DOC per passenger mile per nautica. l rnle = гаП^х^^І^^^ ■