Cost Estimation in Aircraft Design Questions and Answers

Answer: A

It covers everything spent before the first production aircraft is delivered, from concept studies through flight test. Because it is incurred once, spreading it over a larger production run is what makes each aircraft cheaper.

Answer: B

Correct answer: RDT&E, production, operating and disposal

Life cycle cost is the total cost of an aircraft from concept to retirement, comprising research, development, test and evaluation; production; operation and support; and disposal.

The reason for taking all four together is that they trade against one another. Spending more in development on a lighter structure or a more efficient engine raises RDT&E and production cost but reduces fuel and maintenance over decades of service - and since operation and support typically dominate the total, that is usually a good trade. Any narrower definition hides exactly those trades.

Answer: C

Correct answer: Empty weight and speed

In the DAPCA family of models engineering hours are estimated from empty weight and maximum speed, both raised to fitted exponents. Weight stands for the sheer quantity of structure and system to be designed and analysed; speed stands for the technical difficulty, since a faster aircraft demands more aerodynamic, thermal and structural work per kilogram.

Range and passenger capacity influence cost only through their effect on weight, and wing area alone captures neither the whole airframe nor its difficulty. The same two variables drive the tooling and manufacturing relations.

Answer: D

Correct answer: Each doubling of output costs 80 per cent of the last

A learning curve is defined on doublings of cumulative output, not on individual units. An 80 per cent curve means the hundredth unit costs 80 per cent of the fiftieth, the two-hundredth 80 per cent of the hundredth, and so on:

\[ C_n = C_1 n^{\log_2 0.8} = C_1 n^{-0.322} \]

Because doublings become progressively harder to achieve, most of the saving arrives early: the eighth unit already costs \( 0.8^3 = 0.512 \) of the first, but reaching half that again would take another 56 aircraft.

Answer: A

Correct answer: Aircraft depreciation

Depreciation is a fixed cost: the aircraft loses value with time whether it flies or stands on the ramp, and the charge is set by the acquisition price, the depreciation period and the residual value rather than by utilisation.

The other three are variable, accruing only when the aircraft operates - fuel burnt in flight, landing fees charged per movement, and maintenance labour driven by flight hours and cycles. The distinction is what makes utilisation so important: fixed costs per block hour fall as flying hours rise, while variable costs per hour do not.

Answer: B

Correct answer: Administration and marketing

Direct operating cost covers what it takes to fly the aircraft - fuel, flight and cabin crew, maintenance, depreciation, insurance and landing and navigation fees. Administration and marketing are indirect, supporting the airline as a business rather than any particular flight.

The distinction matters because direct operating cost is the figure used to compare aircraft types: it isolates what the aeroplane costs to operate from what the airline costs to run, so two carriers with very different overheads can still compare the same aircraft on a common basis.

Answer: C

Correct answer: Cumulative revenue equals cumulative cost

The breakeven quantity is the number of aircraft at which cumulative revenue finally covers cumulative cost, including the development spend incurred before the first delivery.

\[ N_{BE} = \frac{\text{fixed cost}}{\text{margin per aircraft}} \]

It is the central figure in a programme's business case, because until it is passed the programme has consumed cash without returning it. For a large transport it commonly runs to several hundred aircraft, which is why so few programmes are launched and why launch orders matter so much.

Answer: D

Correct answer: Reduces amortised development cost

RDT&E is a one-off expense incurred before the first delivery, so dividing it over more aircraft reduces the share each must carry:

\[ \text{amortised cost} = \frac{\text{RDT\&E}}{N} \]

A \( 2.4 \) billion dollar development spread over 300 aircraft adds 8 million dollars each; over 600 it adds only 4 million. The total programme cost rises with quantity because more aircraft are built, but the unit production cost falls through learning as well, so both effects push unit cost down as the run lengthens.

Answer: A

At typical fuel prices it is the single largest line, ahead of maintenance and crew, which is why specific fuel consumption dominates the design brief. Its share swings widely with the oil price and is recalculated whenever fuel moves sharply.

Answer: B

Correct answer: Fixed costs are spread over more flying hours

Depreciation, insurance and financing accrue with the calendar rather than with use, so an aircraft flying 3000 block hours a year carries the same annual fixed charge as one flying 2000 - but spreads it over half as much again. Fixed cost per block hour falls in direct proportion.

Nothing else in the list follows. Crew salaries and fuel burn per hour are unchanged, and maintenance intervals set in hours or cycles come round sooner, not later. High utilisation is the low-cost carrier's central lever precisely because of this arithmetic.