TM  1-1520-240-10            2-3-3 712   Power to operate the beep trim system is supplied by the DC and AC buses. DC power to operate a trim motor in the power turbine control box, which unbalances a control circuit, is supplied by the corresponding No. 1 or No. 2 DC buses through the ENGINE NO. 1 or NO. 2 TRIM circuit breakers on the No. 1 or No. 2 PDP. The unbalanced control circuit causes the AC power from the No. 1 or No. 2 AC buses through the ENGINE NO. 1 or NO. 2 TRIM & TIMER circuit breakers on the No. 1 or No. 2 PDP to be transformed and rectified to DC voltage. This DC power operates the power turbine actuator on the engine fuel control. NOTE No   two   engines   provide   matched   perfor- mance with regard to torque, RPM, PTIT, or fuel flow. With torque matched all other pa- rameters may not be matched. 712   Holding the No. 1 & 2 switch forward (RPM IN- CREASE) will increase the RRPM. Holding the switch aft (RPM DECREASE) will decrease the RRPM. When the switch is released, it returns to the center or neutral posi- tion. The switch electrically controls both power turbines by movement of the N2 actuator through each engine power turbine control box. The procedure for matching engine load requires that NO. 1 & 2 engine beep switch be used in conjunction with NO. 1 engine beep switch. When NO. 1 engine beep switch is moved forward (RPM INCREASE), the torque of No. 1 engine increases. At the same time RRPM in- creases, even though No. 2 engine torque decreases slightly. Moving NO. 1 & 2 engine beep trim switch aft (RPM DECREASE) causes both engine torques to de- crease   and   reduce   RRPM.   If   torques   are   still   not matched, this procedure is continued until torques are matched and desired RRPM is attained. The opposite action occurs when NO. 1 engine beep switch is moved aft. The engine beep trim switches should not be used during power changes initiated by thrust lever movement be- cause RRPM droop should only be momentary. The en- gine beep trim system adjusts engine RPM only if the respective ENG COND lever is at FLT. At STOP or GND, it is possible to move the power turbine lever by moving the engine beep trim switches to RPM DECREASE or RPM INCREASE, but in either case, engine RPM will not be affected because the engine is not operating in the N2 governing range. 2-3-10.  EMERG ENG TRIM Panel  712 The EMERG ENG TRIM (emergency engine) panel is located on the center console (fig, 2-3-2). The panel con- sists of two guarded normal engine trim system disabled switches  and  two  momentary  emergency  engine  trim switches. a. Normal Engine Trim System Disable Switches.  The guarded switches permit the pilot to dis- able either or both normal beep trim systems. This pre- vents unwanted signals from the normal beep trim sys- tem  to  interfere  with  the  operation  of  the  emergency engine trim system. Each switch is labeled AUTO and MANUAL. When either switch is at MANUAL, the respec- tive normal beep trim system is disabled (115-volt AC from AC bus to the engine power turbine control box is interrupted). When the switch is at AUTO (cover down), the normal beep trim system is functional (115-volt AC from the AC bus is reconnected to the associated engine power turbine control box). Refer to Chapter 9 for emer- gency engine trim operation. CAUTION Engine  response  is  much  faster  when RRPM  is  controlled  with  emergency  en- gine  beep  trim  system.  It  is  possible  to beep the rotor speed below safe operating speed and low enough to disconnect the generators  from  the  buses.  The  genera- tors   are   disconnected   at   85%   to   82% RRPM after a 3 to 7 second time delay. b. Emergency  Engine  Trim  Switches.  Each  mo- mentary  switch  is  used  to  change  the  power  turbine speed of its respective engine if the power turbine control box (normal beep trim system) malfunction. When the normal trim system fails, the droop eliminator also fails to function. Both switches have an INC, DECR, and  spring-loaded  center  position.  When  one  of  the switches is held at INC, power from the essential DC bus goes  directly  to  the  respective  power  turbine  actuator and increases the lever setting and the power turbine speed. When the switch is held at DECR, the lever set- ting is decreased, and the power turbine speed is de- creased. The  emergency  engine  trim  switches  are  to  be  used when the normal beep trim system is disabled. If one of the switches is used while the respective power turbine control  box  is  functioning  normally,  the  power  turbine actuator setting will temporarily change but will return to its original setting when the switch is released. Power to operate the emergency engine beep trim switches and actuators is supplied by the essential DC bus through the NO. 1 and NO. 2 EMERG ENG TRIM circuit breakers on the No. 1 and No. 2 PDP.