Designing airframes, engines, avionic and electrical circuitry and their subsequent modifications is one of the worlds best guessing games based mainly on lessons learned from previous accidents and incidents where resulting investigations could reliably form positive root causes.
The mere fact that these particular frames have undergone bridging checks in order to transfer ownership as well as (properly approved) heavy modifications does not make them perfect. They can only be considered less imperfect than they were before the Mods / Checks.
The fact that the 707/135 series has (as stated on this thread) undergone so many severe structural changes during their normal development life is..."a concern" to me.
But then, what do I know? I won't be flying in them or responsible for them in any way. I have enough other "used" aircraft to care about.
Last edited by Rigga; 19th May 2013 at 19:56.