Design Requirements and Specifications Questions and Answers

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 give the standard distinction: verification asks whether the product was built right, validation whether the right product was built. Statement 3 claims far too much. An aircraft can meet every requirement and still fail commercially, because the requirements themselves may have been aimed at a market that did not exist - which is exactly the failure validation is meant to catch, and early.

Answer: B

Correct answer: A-2, B-1, C-4, D-3

Certification requirements are absolute: they are the price of being permitted to fly, and no trade study may weigh them against anything. Customer requirements are negotiable and are properly the subject of trades. Derived requirements are flowed down from higher-level ones, and their traceability upward is what allows a change at the top to be followed through. Design constraints are the physical facts of the world, such as gate boxes and pavement strength.

Answer: C

Correct answer: A-2, B-1, C-4, D-3

The diagram reads left to right. The flat portion carries maximum payload while fuel is added freely, since the take-off weight limit has not yet been reached. The first corner is where that limit is reached. The sloping portion then trades payload for fuel one kilogramme for one, holding the weight constant. The second corner is where the tanks are full, beyond which range can only be extended by removing weight altogether, and the line falls more steeply.

Answer: D

Correct answer: A-2, B-4, C-1, D-3

Each requirement shapes a different part of the design. A short field demands low wing loading and high thrust, sizing the wing and the engines. Long range demands a high fuel fraction and a high lift-to-drag ratio, which shape the tanks and the aerodynamics. The airport gate box fixes the span, and hence whether the tip must fold. Noise limits drive the bypass ratio and the acoustic treatment of the nacelle.

Answer: A

Correct answer: A-2, B-4, C-1, D-3

Verification confirms the product meets its specification; validation confirms the specification was the right one. Flow-down is the derivation of lower-level requirements from higher-level ones, which is how an aircraft-level range requirement becomes a fuel system capacity and a structural weight target. Requirements creep is the accumulation of additions after the baseline is set.

Answer: B

Correct answer: A-2, B-1, C-4, D-3

Each decision buys one thing at the price of another. A derivative gives up the optimum configuration for lower development cost and risk. A folding wingtip gives up simplicity to keep aerodynamic span within the gate box. An early design freeze gives up further optimisation for a stable basis on which detail design can proceed. High commonality gives up each variant’s individual optimum for lower operator training and spares costs.

Answer: C

Material selection is a design solution arrived at much later, not a requirement imposed at the outset. Writing it into the top-level set would embed a solution and foreclose alternatives before any analysis had been done.

Answer: D

Correct answer: It specifies how to achieve it

A requirement should state what must be achieved, leaving the solution to the design team. Specifying how forecloses alternatives before they have been examined and confuses the need with one answer to it. The other three are all marks of a good requirement: verifiable, unambiguous, and expressed as an outcome. To these are usually added that it be necessary, achievable and traceable to a higher-level need.

Answer: A

Correct answer: They can be traded away if the customer agreed

This is the incorrect statement. Certification requirements are not the customer’s to waive: they are set by the airworthiness authority, and an aircraft that does not meet them cannot be operated at all, whatever the customer may prefer. They are agreed with the authority at the outset as the certification basis, and they enter the design as absolute constraints rather than as tradeable attributes.

Answer: B

Correct answer: Improved cruise efficiency

Short field performance and cruise efficiency pull in opposite directions. A short field needs a large wing and large engines, and both hurt the cruise - more skin friction, more weight, engines away from their best point. The other three do follow: lower wing loading, higher installed thrust, and a heavier undercarriage to absorb the higher sink rates and shorter ground roll the requirement implies.