I'm going for the easy one first.......
411A, you were here when the L1011's were NEW????? I think that I was still in diapers. Anway the assumed thrust procedures remained the same until the aircraft were retired. Due to the environment and the route structure, it was the only way of keeping the RB211's on the wings. Its only the newer Seattle built Boeings that have increased the temperature band to 69C. Obviously between 54C and 69C can only be used for assumed thrust and not as an extended environmental envelope.
All the best.
Mutt
