Short-haul aircraft reach fatigue-related life limits sooner than long-haul aircraft because
Answer: A
A regional aircraft may fly six or eight sectors a day against a long-haul aircraft's one, so it accumulates pressurisation cycles far faster for the same hours. Life limits for such airframes are therefore quoted in cycles.
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A structural repair to a fatigue-critical area must
Answer: B
An over-stiff patch attracts load and can create a worse concentration at its own boundary than the damage it repaired. Repair design is therefore about matching stiffness and easing the transition, not simply about adding material.
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An aircraft flies \( 6 \) sectors a day for \( 300 \) days a year. Its annual pressurisation cycle count is
Answer: C
Correct answer: 1800
\[ 6 \times 300 = 1800\ \mathrm{cycles\ per\ year}. \] Each sector is one pressurisation cycle, and it is the cycles rather than the hours that consume the fuselage’s fatigue life - which is why the certified life of a transport structure is quoted in cycles as well as hours.
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A long-haul aircraft flies \( 1 \) sector a day for \( 300 \) days. Compared with the short-haul case, it reaches the same cycle count in
Answer: D
Correct answer: Six times as many years
The long-haul aircraft accumulates 300 cycles a year against the short-haul aircraft’s 1,800, so it takes six times as long to reach the same count. This is the reason a short-haul fleet flying identical airframes ages far faster in fatigue terms, and why cycle count rather than calendar age governs the inspection programme.
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Assertion (A): The Comet investigation reshaped how transport fuselages are certified.
Reason (R): It established that repeated pressurisation could crack a structure comfortably strong statically.
Select the correct answer from the options below.
Answer: A
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. The Comet fuselages failed from cracks that started at cut-outs and grew under repeated cabin pressurisation, in a structure that was entirely adequate under static test. The investigation established pressurisation fatigue as a first-order design case and led directly to full-scale fatigue testing of transport fuselages.
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Assertion (A): A fatigue repair patch should not be made as stiff as possible.
Reason (R): An over-stiff patch attracts load and creates a concentration at its own boundary.
Select the correct answer from the options below.
Answer: B
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. Load flows to stiffness, so a patch much stiffer than the skin it repairs draws load into itself and dumps it back at its own boundary, creating a fresh concentration and simply moving the cracking outboard. A good repair is matched in stiffness and tapered at its edges to spread the transfer.
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Consider the following statements about ageing aircraft:
1. Widespread fatigue damage becomes more likely with accumulated cycles.
2. Corrosion and fatigue interact to shorten life.
3. Calendar age alone determines the structural condition.
Which of the statements given above is or are correct?
Answer: C
The first two are correct. The third ignores utilisation: an aircraft flying six short sectors a day accumulates cycles six times faster than one flying a single long sector, so cycles rather than years govern much of the damage.
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Consider the following statements about fatigue substantiation testing:
1. A full-scale article is cycled through a representative load spectrum.
2. A scatter factor is applied to the demonstrated life.
3. The test may be stopped once the design service life is reached.
Which of the statements given above is or are correct?
Answer: D
The first two are correct. The third would leave no margin: the test is run to several times the intended life precisely so that the scatter factor can be applied and the certified life still cover the service requirement.
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Match each historical event or programme in List I with what it established in List II.
List I
A. Comet accidents
B. Aloha Airlines 243
C. Ageing aircraft programmes
D. Damage tolerance rules
List II
1. Widespread fatigue damage in a high-cycle airframe
2. Pressurisation fatigue as a first-order design case
3. Crack growth analysis setting inspection intervals
4. Systematic inspection of high-cycle fleets
Select the correct match.
Answer: A
Correct answer: A-2, B-1, C-4, D-3
Four points in the same history. The Comet accidents established pressurisation fatigue as a first-order design case; Aloha 243, where a section of upper fuselage separated in flight, demonstrated widespread fatigue damage in a very high-cycle airframe; the ageing aircraft programmes that followed instituted systematic inspection of high-cycle fleets; and the damage tolerance rules made crack growth analysis the basis for setting the intervals.
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Which of these is NOT a reason fuselage fatigue life is quoted in cycles rather than hours?
Answer: B
The differential is set by cruise altitude, not by how long the flight lasts, so a two-hour and a twelve-hour sector apply much the same cycle. The other three are exactly why cycles rather than hours are the meaningful measure.
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