XPDR 5537 IDNT LCL23:00:34 $_{5}$338 $_{1}$1652 200 46 13.7 2300 23.0 VOR 1 270 ° 2 1 1 2 4 300 4 200 4 100 4 000 3 900 3 800 4300 3600 3500 3400 3300 3200 3100 60 20 000 130 120 110 90 80 70 1 100 9 TAS 100KT ALERTS NAV1 108.00 113.00 NAV2 108.00 110.60 134.000 118.000 COM1 123.800 118.000 COM2 $_{WPT }$_ _ _ _ _ _$_{ DIS }$_ _ ._ $_{NM}$ $_{DTK }$_ _ _$_{°}$ TRK 360° 5 338 $_{1}$1652 200 46 13.7 2300 23.0 NAV1 108.00 113.00 NAV2 108.00 110.60 Figure 14-4.  Powerplant instrumentation—fixed shaft turboprop engine. of the propeller blades automatically toward their feathered  position should the engine suddenly lose power while in  flight. The NTS system is an emergency backup system in  the event of sudden engine failure. It is not a substitution  for the feathering device controlled by the condition lever. Torque developed by the turbine section is measured by a  torque sensor. The torque is then reflected on the instrument  panel horsepower gauge calibrated in horsepower times 100.  ITT is a measurement of the combustion gas temperature  between the first and second stages of the turbine section. The  gauge is calibrated in degrees Celsius (°C). Propeller rpm is  reflected on a tachometer as a percentage of maximum rpm.  Normally, a vernier indicator on the gauge dial indicates  rpm in 1 percent graduations as well. The fuel flow indicator  indicates fuel flow rate in pounds per hour. In a free power-turbine engine, such as the Pratt & Whitney  PT-6 engine, the propeller is driven by a separate turbine  through reduction gearing. The propeller is not on the  same shaft as the basic engine turbine and compressor.  [Figure 14-5]  Unlike the fixed shaft engine, in the split  shaft engine the propeller can be feathered in flight or on the  ground with the basic engine still running. The free power- turbine design allows the pilot to select a desired propeller  governing rpm, regardless of basic engine rpm. Propeller feathering in a fixed shaft constant-speed turboprop  engine is normally accomplished with the condition lever.  An engine failure in this type engine, however, results in a  serious drag condition due to the large power requirements of  the compressor being absorbed by the propeller. This could  create a serious airplane control problem in twin-engine  airplanes unless the failure is recognized immediately and  the affected propeller feathered. For this reason, the fixed  shaft turboprop engine is equipped with negative torque  sensing (NTS). A typical free power-turbine engine has two independent  counter-rotating turbines. One turbine drives the compressor,  while the other drives the propeller through a reduction  gearbox. The compressor in the basic engine consists of  three axial flow compressor stages combined with a single  centrifugal compressor stage. The axial and centrifugal stages  are assembled on the same shaft and operate as a single unit. NTS is a condition wherein propeller torque drives the engine,  and the propeller is automatically driven to high pitch to  reduce drag. The function of the negative torque sensing  system is to limit the torque the engine can extract from the  propeller during windmilling and thereby prevent large drag  forces on the airplane. The NTS system causes a movement  Inlet air enters the engine via a circular plenum near the  rear of the engine and flows forward through the successive  compressor stages. The flow is directed outward by the  14-5 Split Shaft/ Free Turbine Engine 