Pylon and nacelle control Power levers Control rods Wing front span Center console IDLE MAX INC INC RPM adjustment 0.125 hex socket 0.1875 hex socket Figure 8-14.  Typical fuel control adjustments.  Figure 8-13.  Power lever control system.  of the adverse effects on trimming accuracy. To obtain the  most accurate results, the aircraft should always be headed  into the wind while the engine is being trimmed. With the aircraft headed into the wind, verify that the exhaust  area is clear. Install an engine trim gauge to the T-fitting in the  turbine discharge pressure line. Start the engine and allow it  to stabilize for 5 minutes before attempting to adjust the fuel  control. Refer to the applicable manufacturer’s instructions  for correct trim values. Compensate for temperature and  pressure during the trimming process. If a hydromechanical  fuel control is not within limits, turn the INC. MAX screw  [Figure 8-14]  about one-eighth turn in the appropriate  direction. Repeat, if necessary, until the desired value is  attained. If the aircraft is equipped with a pressure ratio gauge,  set it to the correct value. An example of a trim check using an electronic controlled  fuel control must take into account temperature and pressure  for each parameter measured. The parameters checked can  include: carefully inspecting for adequate clearance between the  various push-pull rods and tubes. Secure all locknuts, cotter  pins, and safety as required. The fuel control unit of the typical turbofan on older aircraft  can be a hydromechanical device that schedules the quantity  of fuel flowing to the engine so that the desired amount of  thrust can be obtained. The amount of thrust is dictated by the  position of the power lever in the cockpit and the particular  operation of the engine. Thus, the thrust of the engine and  the consequent rpm of its turbine are scheduled by fuel flow. The fuel control unit of the engine is adjusted to trim the  engine to obtain maximum thrust output of the engine when  desired. The engine must be retrimmed after a fuel control  unit is replaced, the engine does not develop maximum thrust,  engine change, or excessive throttle stagger. After trimming the engine, the idle rpm can be adjusted.  The idle rpm is adjusted by turning the INC. IDLE screw an  eighth of a turn at a time, allowing sufficient time for the rpm  to stabilize between adjustments. Retard the power lever to  idle and recheck the idle rpm. If wind velocity is a factor, the aircraft should be headed  into the wind while trimming or checking the trim on an  engine. Since trimming accuracy decreases as windspeed  and moisture content increase, the most accurate trimming is  obtained under conditions of no wind and clear, moisture-free  air. Do not trim when there is a tailwind because hot exhaust  gases may be reingested. As a practical matter, the engine  should never be trimmed when icing conditions exist because  Adjusting the Fuel Control 1. Minimum idle (percent N$_{2}$) 2. Approach idle (percent N$_{2}$) 3. 2.5 bleed open (percent N$_{1}$) 4. 2.5 bleed closed (percent N$_{1}$) 5. Takeoff engine pressure ratio (EPR) 6. 95 percent takeoff thrust (EPR) 7. 90 percent thrust change decal (EPR) 8-15