Engine run-up de-icing
In the early days of the B757, severe weather run-up was 60%N1 for 60 secs every 60 mins. It was normal then to release brakes and start the T/O run (running, as it were). After some incident, Rolls examined the matter (RB211-535C) and revised the procedure to 60% N1 for 10 secs followed by a sharp reduction to idle before commencing T/O. The Management notice to this effect said that the rationale was that the ice shedding was accomplished by the twisting of the fan blades as they changed from forward thrust to idle. It was (not quite tacitly) admitted that all the previous one minute shuddering at 60 % N1 had been in vain.
During a recent sim session with a company using 535C engines, I found that their SOP's did NOT require the reduction to idle before starting T/O.
My question is: has the original lesson been over-ridden, or just lost in history? Also, would this apply to the E4 (and others) as well?
Any help, chaps?
Prober