An engineer designs a wing box using multiple spars, stringers, and skin panels so that if any single structural member completely fails, the remaining structure can still carry the load until the damage is detected during a scheduled inspection. Which structural design philosophy does this describe?
- ASafe-life design
- BFail-safe design
- CDamage-tolerant design
- DMonocoque design
Show answer & explanationAnswer & explanation
Correct answer: B. Fail-safe design
Fail-safe design provides multiple redundant load paths so that the failure of one structural member does not lead to catastrophic failure of the entire structure, allowing the remaining members to carry the load until the failure is found and repaired. Safe-life design instead relies on retiring parts before they reach a calculated failure point, and damage-tolerant design assumes cracks exist and relies on inspection intervals to catch crack growth before critical size.
Why the other options are wrong
- A. Safe-life design retires components before a predicted fatigue life is reached, rather than relying on redundant load paths.
- C. Damage-tolerant design assumes initial flaws exist and relies on inspection to detect crack growth, which is a related but distinct philosophy.
- D. Monocoque design uses the skin alone to carry all structural loads, with no internal framework redundancy.
Fail-Safe Design
A structural design philosophy using multiple redundant load paths so that failure of one member does not cause overall structural failure, allowing continued safe flight until detected.
- Uses redundant load paths (multiple spars, stringers, etc.)
- Failure of one member is tolerated
- Different from safe-life (retirement) and damage-tolerant (inspection-based crack monitoring) philosophies
Memory trick: Fail-Safe = if one path Fails, others stay Safe.