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Aircraft undergo regular preventative maintenance checks, with letter codes A - D. The D check being the most comprehensive, it occurs every 6-10 years and basi

Aircraft undergo regular preventative maintenance checks, with letter codes A - D. The D check being the most comprehensive, it occurs every 6-10 years and basically the entire aircraft is taken apart and inspected, looking for among other things anything like stress fractures, corrosion, unusual wear, etc. https://en.wikipedia.org/wiki/Aircraft_maintenance_checks#D_check https://en.wikipedia.org/wiki/Aircraft_maintenance_checks#D_... A commercial aircraft does not just accumulate wear and tear for 25 years until something breaks. They can basically fly indefinitely, but in reality after two or three D checks they are usually retired because the cost of the D check is more than the value of the aircraft.

ghotli 6y ago
Great context. I gained a lot of respect for aviation's use of checklists and procedures from the book 'The Checklist Manifesto' In this case, something obviously went awry and it's both engineering, planning, and a miracle no one died or was crushed from debris from above. Regardless, comments like yours leave me feeling far more confident in this sort of thing.
- eru 6y ago
  > In this case, something obviously went awry and it's both engineering, planning, and a miracle no one died or was crushed from debris from above. [...] Yes, though even something going wrong doesn't necessarily mean that we'd need to change any procedures. Sensible procedures bring risks down to acceptable levels at an acceptable price. That level of risk is generally still more than 0%.
touisteur 6y ago
Beware of the dangers of preventative maintenance, where sometimes while replacing or inspecting or re-mounting inspected parts, the maintenance crew breaks something that was OK and probably going to be working fine for years. But yeah, a D check is so expensive I've heard there's a habit of dumping the aircraft on less observing flying companies some thousand miles before it comes up...
- Leherenn 6y ago
  A minor point, it's not based on miles, but cycles (takeoffs/landings) for structural parts or hours for engines.
  - touisteur 6y ago
    You're right, thanks for the correction.
dzhiurgis 6y ago
> basically the entire aircraft is taken apart How is that safe unless you've got a production line doing it? Seems impossible to re-assemble it in the same way as it was done in factory...
- donarb 6y ago
  It's not taken totally apart, but it is stripped of the interior down to the bare metal, all wiring is checked/replaced as needed. All mechanical parts like the flaps and landing gear are removed and checked for wear. The skin is checked for cracks. This is done every 5 years for planes, taking about 5-6 weeks to complete. Here's https://www.youtube.com/watch?v=WLil1MZmchI https://www.youtube.com/watch?v=WLil1MZmchI
pdonis 6y ago
> Aircraft undergo regular preventative maintenance checks And in a similar incident in February 2018 on a 777 (referred to upthread), one of those checks was found to have failed: the NTSB determined that the root cause was a cracked engine fan blade that should have been detected on a previous inspection (and that would have resulted in the blade being replaced), but wasn't. If this incident turns out to have a similar root cause, that means there are issues with the preventive inspection and maintenance process.

ghotli 6y ago

Great context. I gained a lot of respect for aviation's use of checklists and procedures from the book 'The Checklist Manifesto' In this case, something obviously went awry and it's both engineering, planning, and a miracle no one died or was crushed from debris from above. Regardless, comments like yours leave me feeling far more confident in this sort of thing.

eru 6y ago
> In this case, something obviously went awry and it's both engineering, planning, and a miracle no one died or was crushed from debris from above. [...] Yes, though even something going wrong doesn't necessarily mean that we'd need to change any procedures. Sensible procedures bring risks down to acceptable levels at an acceptable price. That level of risk is generally still more than 0%.

touisteur 6y ago

Beware of the dangers of preventative maintenance, where sometimes while replacing or inspecting or re-mounting inspected parts, the maintenance crew breaks something that was OK and probably going to be working fine for years. But yeah, a D check is so expensive I've heard there's a habit of dumping the aircraft on less observing flying companies some thousand miles before it comes up...

Leherenn 6y ago
A minor point, it's not based on miles, but cycles (takeoffs/landings) for structural parts or hours for engines.
- touisteur 6y ago
  You're right, thanks for the correction.

dzhiurgis 6y ago

> basically the entire aircraft is taken apart How is that safe unless you've got a production line doing it? Seems impossible to re-assemble it in the same way as it was done in factory...

donarb 6y ago
It's not taken totally apart, but it is stripped of the interior down to the bare metal, all wiring is checked/replaced as needed. All mechanical parts like the flaps and landing gear are removed and checked for wear. The skin is checked for cracks. This is done every 5 years for planes, taking about 5-6 weeks to complete. Here's https://www.youtube.com/watch?v=WLil1MZmchI https://www.youtube.com/watch?v=WLil1MZmchI

pdonis 6y ago

> Aircraft undergo regular preventative maintenance checks And in a similar incident in February 2018 on a 777 (referred to upthread), one of those checks was found to have failed: the NTSB determined that the root cause was a cracked engine fan blade that should have been detected on a previous inspection (and that would have resulted in the blade being replaced), but wasn't. If this incident turns out to have a similar root cause, that means there are issues with the preventive inspection and maintenance process.