Posted: Sat Nov 28, 2015 4:16 pm Post subject: Reference EPR
Need a little bit of help to understand Reference EPR on B757 / 767 PW equipped.
I understand that the Max EPR is the maximum EPR under all phases of flight. I understand that setting TO, CLB, CRZ, etc on the TMSP then sets the reference EPR.
What I don't understand is what this reference EPR means. Is it the EPR limit the EEC will hold with full forward throttle with the particular TMSP setting? Or is it simply a maximum preferred indication for the TMSP selected setting? Or, is it something else.
I give you an example regarding B777, it might help.
Pressing TOGA on ground, below 50 knots activates autothrottle in the THR REF mode i.e. the reference thrust limit selected on THRUST LIMIT page of FMC (we dont have TMSP, but the concept is the same as I believe its the same as TRP we had on A310). So the throttles follow the reference whatever it is and the reference is set by FMC/TMSP etc.
Pressing TOGA on approach activates autothrottle in THR mode only whereas the GA reference thrust limit calculated by FMS is just displayed and not followed. This use of less (than the reference) thrust is to give 2000 feet per minute climb. However the second push activates autothrottle in THR REF mode i.e. using GA reference thrust as calculated by the FMC.
Thrust management calculates a reference thrust for the following thrust settings:
TO – Takeoff
TO1 – Takeoff one
TO2 – Takeoff two
D–TO – Assumed temperature takeoff
D–TO1 – Derate one assumed temperature takeoff
D–TO2 – Derate two assumed temperature takeoff
CLB – Climb
CLB 1 – Climb one
CLB 2 – Climb two
CRZ – Cruise
CON – Continuous
G/A – Go–around.
In case of B777 full throttles will not be used for some references like for derate takeoffs. This is indicated in its manual that says:
With both TO1 and TO2, the thrust setting parameter is considered a limitation for takeoff; therefore, thrust levers should not be advanced further except in an emergency.
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