Nope, don't think it's dodgy - my understanding is that it is actually the right thing to do. Remember that what you are doing with the N1 / EPR comparison is ensuring that you are producing the amount of power that you AUGHT to be doing, ie ensuring that the PT2 probe is not blocked, giving you a higher EPR than that which should be associated with a given N1 value.
So, you have already decided through the use of reduced thrust that available runway is consistent with with the actual TOW and that this can be achieved with a reduced EPR (assumed higher OAT). You have hence decided to advance the thrust levers only far enough forward to produce this REDUCED EPR, and therefore the comparison should be with the reduced EPR and not a higher EPR setting (actual OAT) that you have decided to only use in the event of loss of engine thrust on one engine.
Sorry - this is probably clumsily formulated, but the crosscheck is to make sure that you are getting the thrust out of the engine that you have computed to get with the power seetting ACTUALLY used for takeoff. The N1 crosscheck serves to validate the EPR you have chosen to use.
Hope that helps.
Last edited by Guppy Driver; 12th February 2006 at 09:36.