by the absence of air mixed in the fuel emerging from the end  of the hose submerged in the container of fuel. Air trapped in  the system should not be confused with the numerous small  air bubbles that may appear as a result of the velocity of the  fuel being ejected from the engine’s fuel unit. Usually, after  approximately a gallon of fuel has been bled off, the system  can be considered safe for operation. After completing the  bleeding operation, return all switches and controls to their  normal, or off, position, and replace and safety all fuel unit  connections disturbed. The propeller, if equipped, must be checked before, during,  and after the engine has been ground operated. The propeller  should be checked for proper torque on the mounting bolts,  leaks, vibration, and for correct safety. A propeller whose pitch-changing mechanism is electrically  actuated may be checked before the engine is operated.  Propellers whose pitch-changing mechanisms are oil actuated  must be checked during engine operation after the normal  operating oil temperature has been reached. In addition to  checking the increase or decrease in rpm, the feathering cycle  of the propeller should also be checked. After the engine has been ground operated, and again after  flight test, operational factors must be adjusted, as necessary,  and the entire installation given a thorough visual inspection.  These adjustments often include fuel pressure and oil pressure,  as well as rechecks of such factors as ignition timing, valve  clearances, and idle speed and mixture. If these rechecks are  indicated by the manner in which the engine performs. After both the initial ground runup and the test flight, remove  the oil sump plugs and screens and inspect for metal particles.  Clean the screens before reinstalling them. Check all lines for leakage and security of attachment.  Especially, check the oil system hose clamps for security  as evidenced by oil leakage at the hose connections. Also,  inspect the cylinder holddown nuts or cap screws for security  and safety. This check should also be performed after the  flight immediately succeeding the test flight. The following instructions cover some of the basic  inspections and procedures for rigging and adjusting fuel  controls, fuel selectors, and fuel shutoff valves. 1.  Inspect all bellcranks for looseness, cracks, or  corrosion. 2.  Inspect rod ends for damaged threads and the number  of threads remaining after final adjustment.  3.  Inspect cable drums for wear and cableguards for  proper position and tension. While rigging the fuel selector, power controls, and shutoff  valve linkages, follow the manufacturer’s step-by-step  procedure for the particular aircraft model being rigged.  The cables should be rigged with the proper tension with  the rigging pins installed. The pins should be free to be  removed without any binding; if they are hard to remove, the  cables are not rigged properly and should be rechecked. The  power lever should have the proper cushion at the idle and  full-power positions. The pointers, or indicators, on the fuel  control should be within limits. The fuel selectors must be  rigged so that they have the proper travel and do not restrict  the fuel flow to the engines. Many older conventional turbofan engines use various power  lever control systems. One of the common types is the cable  and rod system. This system uses bellcranks, push-pull rods,  drums, fairleads, flexible cables, and pulleys. All of these  components make up the control system and must be adjusted  or rigged from time to time. On single-engine aircraft, the  rigging of the power lever controls is not very difficult. The  basic requirement is to have the desired travel on the power  lever and correct travel at the fuel control. On multiengine  turbojet aircraft, the power levers must be rigged so that they  are aligned at all power settings. Most computer controlled engines have an electronic  connection from the flight deck to the engine. This eliminates  the need for any type of cable or linkages. In the computer  controlled system, the computer sends electronic information  through wires or buses to the fuel control to command it to  follow pilot inputs from the flight deck. On older style aircraft the power lever control cables and  push-pull rods in the airframe system to the pylon and nacelle  are not usually disturbed at engine change time and usually  no rigging is required, except when some component has  been changed. The control system from the pylon to the  engine must be rigged after each engine change and fuel  control change.  Figure 8-13  shows the control system from  the bellcrank in the upper pylon to the fuel control. Before adjusting the power controls at the engine, be sure  that the power lever is free from binding and the controls  have full throw on the console. If they do not have full throw  or are binding, the airframe system should be checked, and  the discrepancies repaired. After all adjustments have been  made, move the power levers through their complete range,  Propeller Check Rigging Power Controls Checks and Adjustments After Engine  Runup and Operation Rigging, Inspections, and Adjustments 8-14