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Fatigue Critical Baseline Strucure 1
- Thread starter CRACKKILZ
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1
- #3
SuperStress
Aerospace
"Safe Life" and "Damage Tolerant" are merely two aircraft lifing paradigms. Safe life designed aircraft (especially older ones) were analyzed using stress-life fatigue analyses. Some newer planes have used strain-life methods. The idea in either case is that some design service goal is determined based on an assumed usage and stress levels, and then parts are retired prior to their safe life being fully expended.
Damage Tolerance assumes an initial flaw and does not take credit for any durability life prior to crack formation. The design service life is determined by crack growth analyses in conjunction with planned inspection intervals. The point of damage tolerance is that no flaw should be able to grow from it's minimum inspectable size to critical within one inspection interval. Some aircraft designed under damage tolerance may still have some safe-life-designed parts (often landing gear).
That's a long explanation to get to the point that any fatigue critical baseline structure should be identified in the list, regardless of the design paradigm of the aircraft.
Let me know if any of that doesn't make sense and I'll try to elaborate.
SuperStress
Damage Tolerance assumes an initial flaw and does not take credit for any durability life prior to crack formation. The design service life is determined by crack growth analyses in conjunction with planned inspection intervals. The point of damage tolerance is that no flaw should be able to grow from it's minimum inspectable size to critical within one inspection interval. Some aircraft designed under damage tolerance may still have some safe-life-designed parts (often landing gear).
That's a long explanation to get to the point that any fatigue critical baseline structure should be identified in the list, regardless of the design paradigm of the aircraft.
Let me know if any of that doesn't make sense and I'll try to elaborate.
SuperStress
Worldtraveller
Aerospace
I don't think Boeing identifies safe life structure on their FCBS either. I suspect the main reason is that the FCBS is generally intended to give a heads up to liaison/service engineering that if they do a repair on FCBS, then extra documentation and sometimes analysis is needed. Most safe life structure can't be repaired (there are a few exceptions I've seen) so it is not on the list.
Different manufacturers may have different arrangements with the FAA though, and it can vary drastically based on the certification date of the aircraft as well.
Different manufacturers may have different arrangements with the FAA though, and it can vary drastically based on the certification date of the aircraft as well.
wouldn't a change to the U/C require compliance to part 26 ?
certainly, the primary intent of part 26 is DTA; i think that part 26 only exists 'cause the FAA did a lousy job implementing 25.571 in the 1st place. but a change to an U/C would have to consider the impact on fatigue, no? if you want it is implicitly FCBS.
Quando Omni Flunkus Moritati
certainly, the primary intent of part 26 is DTA; i think that part 26 only exists 'cause the FAA did a lousy job implementing 25.571 in the 1st place. but a change to an U/C would have to consider the impact on fatigue, no? if you want it is implicitly FCBS.
Quando Omni Flunkus Moritati
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