SASless,
nothing to do with Eket. It was done after an accident in the North Sea in the Eighties. Obviously the Eket machines, beinmg company aircraft, were then fitted too.
The aircraft were not re-modded to the original system; they were modded to the later TB-138/TB-145 state, or HP mod, with a manual beep for the number two engine N2, rather than the TCU doing the matching. At one stage we had all thtree mod states in service in Eket.