Airbus Driver Question:

[Autothrust Blue]

While this is true, you don't just blindly set power by EPR. You need to cross check your N1 to ensure you don't have a faulty probe. You can trash an engine doing that. Low faulty EPR, you push the power up to match EPR, now you just exceeded N1.

Or conversely, the Air Florida crash. Had they looked at their N1 instead of just the EPR, they would have noticed the low power output of the motors.

"Following the lengthy investigation into the Potomac accident, notices were sent to all operators of Pratt & Whitney JT8D series engines, warning that crews should be on alert for erroneous EPR indications in icing conditions and to rely primarily on the engine RPM gauge for actual indications of power. Typically, the RPM gauge is called an N1 or Fan gauge and will usually show 35% N1 while idling, 83% in cruise, and 95% — 101% on takeoff. Blocking of PT2 tubes by substances other than ice was not discussed in the Alert Bulletin."

It's basic pilot stuff.

I've never understood why Pratts use EPR; if the engine is driving the fan at the correct RPM, then you are getting the thrust you expect. (At least, that's what my GE tech rep said.)

 

[Roger Roger]

I've never understood why Pratts use EPR; if the engine is driving the fan at the correct RPM, then you are getting the thrust you expect. (At least, that's what my GE tech rep said.)

Because just like with the PT6 they're still stuck in the 1960s when turbojets were a thing and EPR was a more applicable way of measuring their thrust output.