Yes, obviously; MD-11s aren't flinging engines off the wing every single takeoff. A 34 year old airframe may or may not actually match design strength, though.
Yes, but the point is that this moment of the takeoff is when a failure that's been waiting to happen is most likely both because of the thrust and the gyroscopic resistance.
Did I understand the report correctly that the part was scheduled to be replaced in the future after a certain number of hours, it just hadn't hit the threshold yet ?
If you're referring to this quote (excerpted from the AVHerald article linked elsewhere in the thread), I don't think so:
> At the time of the accident, N259UP had accumulated a total time of about 92,992 hours and 21,043 cycles [..] A special detailed inspection (SDI) of the left pylon aft mount lugs would have been due at 29,200 cycles and of the left wing clevis support would have been due at 28,000 cycles
This isn't talking about replacement, only inspection; and it wasn't going to happen in the near future: 7k cycles at four flights/day means inspection is due in 5 years.
It wasn't doing four flights per day. As a long-distance cargo aircraft it was doing two flights per day, and I doubt it was flying every single day of the week.
So we are talking about at least 10 years before that inspection was due.
I'd be very surprised to read that the aft lug that cracked (and the bearing it contained) were made of aluminum. They were almost certainly steel or Inconel.
I know Veritasium gets posted here a lot, but a few days ago he posted a deep-dive into the the engineering of jet engine turbine blades. Turns out they're made from a single crystal of a superalloy that entangles itself at a molecular level such that it actually gains strength as it's heated, only losing strength above 1200 degrees C / 2200 degrees F. Below that temperature, as long as the strain on the part is below the plastic deformation threshold, it's not really losing any strength at all over time.
No; roughly, yes. Based on the crystal structure of the metal, fatigue works differently.
> The fatigue limit or endurance limit is the stress level below which an infinite number of loading cycles can be applied to a material without causing fatigue failure.[1] Some metals such as ferrous alloys and titanium alloys have a distinct limit,[2] whereas others such as aluminium and copper do not and will eventually fail even from small stress amplitudes.
