The investigations of the accidents/incidents caused by metal fatigue make interesting reading. Of the 6 you mentioned, two were 747s and 4 were 737s. The 737s all had over 30,000 cycles. The most famous of those, the Aloha incident, was a 737 with 89,680 cycles!
Of greater relevance to Baltia are the 747 crashes. In addition to the two 747 accidents you mentioned involving structural failure, there is another famous one: JAL flight 123 on 8/12/1985. None of these three 747 crashes involved high cycle times. Of special interest is the fact that the JAL and the China Airlines disasters involved similar causes: improper repairs of prior tail-strike damage. These improper tail-strike repairs resulted in metal fatigue in the patches that eventually brought catastrophic structural failure in the tails.
There is no record in the NTSB database of the Baltia N706BL / NWA N623US aircraft ever having a tail-strike incident, or any other kind of reportable structural damage.
The El Al 747 flight #1862 that you mentioned was a cargo flight that had two engines fall off the right wing shortly after takeoff. This fatal accident was of particular concern to authorities because this aircraft had only 10,107 cycles and 45,746 hours (not a high time aircraft). The finding in this case was that metal fatigue in a part of an engine mount had prevented engine #3 from breaking away cleanly when the engine started to disintegrate from a mechanical failure. The engine mount was purposely designed to allow the engine to break away cleanly if it vibrates uncontrollably, in order to prevent damage to other parts of the airplane. Instead, a degraded engine mount made engine #3 tear away with difficulty, making it smash into engine #4 and part of the wing. Then engine #4 also broke off, and there was serious flap damage. The plane subsequently rolled over to the right and crashed.
As a result of this El Al crash, 747 engine mounts were redesigned and an AD was issued that required replacement of key engine mount parts on all affected 747s in service. This AD compliance was accomplished on Baltia's N706BL.
AI
