As I understand CX prefers EPR instead of N1 since it is a better indication of thrust (old engines vs new engines). Now, the other day I was reading Jet Airplane Performance by Lufthansa Consulting and found the following:
2.2.11 Thrust Tolerances
It is obvious that engines of a specific series cannot be quite 100% identical after assembly. As a result, it is possible for two engines to produce different thrust levels even at the same N1 or
EPR settings. For this reason, the two thrust definitions 'Average Engine Thrust' and 'Minimum Engine Thrust' were introduced.
While the average thrust is used for all pre-flight calculations of cruise performance, takeoff performance calculations make exclusive use of the manufacture's guaranteed Minimum Engine Thrust.
Would older engines still give guaranteed Minimun Engine Thrust at a certain N1 indication; never mind EPR? And if the trust levels can be different at the same EPR setting (as well as for N1) then why make such a strong case for EPR? I wonder if EPR is that much better than N1 then how come some manufactures donīt provide an EPR indication and only N1 for setting thrust. Or did Lufthanse Consulting get something wrong here?
