SMOC Here is a description + SPITTY42 Well done. During any Engine Start, when the Start Switch is selected to the
Ground Start position, the Control Amplifier is enabled, and runs the
Variable Restrictor to the full trim position, and then back to Normal,
to exercise the variable restrictor located in the HP fuel pump.
If the variable restrictor remains in the full trim position (closed),
Engine start will be normal, however the engine thrust output as the
thrust lever is moved up to the Take Off power range, will be limited
to 1.30 EPR. This is caused by the fuel flow increase being restricted
by the trim valve being modulated into its extended position as the
fuel flow increases. This results in Throttle Stagger which is an
apparent shortfall in the power output of the engine for a particular
throttle lever position.
When operating the eng limit control sw to test this also functions the variable restrictor actuator to reduce fuel flow to the ffr to simulate fuel trimming if you have an N2 approaching overspeed.
Last edited by TRAVENGINEER; 16th September 2006 at 08:11.