From Ignition Override
>Checkboard: I must make an embarassing admission. For all the numerous... years I've flown fanjets, nobody has been able to explain to me just what sort of engine stress is caused by exceeding EPR limits, unless it is some connection between N1 and N2 limits, maybe a combination?
Although this is purely academic and is not required knowledge at this airline, or in Navy Reserve squadrons, from a realistic cockpit perspective (knowing that we do our best to constantly adjust the EPR for the limits, but don't pull it back at our company during takeoff even if EGT is in the yellow arc), it would be interesting to finally understand it.<
Generally speaking its easier to understand the redline limits on N1, N2 and EGT regarding engine stress. However there is also a limit on burner pressure which the fuel control tracks quite nicely.
The only problem that I can ever recall directly attributable to over EPR was the SAS Double Ice ingestion and the AA MD80 double engine woodchipper at Hartford where the extra pressure in the cmpressor coupled with other damage managed to light off the titanium blades in the compressor.
In both cases the EPR signals were confused by significant flow loss out of the damaged fans and an overboost throttle command at the same time.