Fan air Combustion Exhaust Inlet air Combustion F an air Figure 15-2.  Turbofan engine. Figure 15-3.  Jet engine power controls. 15-3 temperature li mits, even for a very few seconds, may result in  serious heat damage to turbine blades and other components.  Depending on  the make and model, gas temperatures can be  measured at a number of different locations within the engine.  The associated engine gauges therefore have different names  according to their location. For instance: turbofan engine increases acceleration, decreases the takeoff  roll, improves initial climb performance, and often has the  effect of decreasing specific fuel consumption. Specific fuel  consumption is a ratio of the fuel used by an engine and the  amount of thrust it produces. In a jet engine, thrust is determined by the amount of fuel  injected into the combustion chamber. The power controls  on most turbojet-and turbofan-powered airplanes consist of  just one thrust lever for each engine, because most engine  control functions are automatic. The thrust lever is linked  to a fuel control and/or electronic engine computer that  meters fuel flow based upon revolutions per minute (rpm),  internal temperatures, ambient conditions, and other factors.  [Figure 15-3] In a jet engine, each major rotating section usually has a  separate gauge devoted to monitoring its speed of rotation.  Depending on the make and model, a jet engine may have an  N$_{1}$ gauge that monitors the low-pressure compressor section  and/or fan speed in turbofan engines. The gas generator  section may be monitored by an N$_{2}$ gauge, while triple spool  engines may have an N$_{3}$ gauge as well. Each engine section  rotates at many thousands of rpm. Their gauges therefore are  calibrated in percent of rpm rather than actual rpm, for ease  of display and interpretation.  [Figure 15-4] The temperature of turbine gases must be closely monitored  by the pilot. As in any gas turbine engine, exceeding  Operating the Jet Engine • Exhaust Gas Temperature (EGT)—the temperature  of the exhaust gases as they enter the tail pipe after  passing through the turbine.