Figure 2-20. Engine Instrument Test Panel

TM 1-1520-238-10 2-32 Change 9 M01-123 Figure 2-20. Engine Instrument Test Panel 2.32.1 Pilot Engine Instruments. All of the pilot en- gine instruments are on the left side of his instrument pan- el. These instruments are tested by the pilot engine instru- ment test panel (fig 2-20). When the switch on the test panel is set at NORM, all instrument lights are operated by their functional inputs. When the switch is set at DGT OFF, all digital displays turn off. When the switch is set at TST, all digital displays indicate 888, and all vertical-scale read- ings are illuminated sequentially from the bottom to full scale for 3 seconds, then extinguish. The following engine instruments are located on the pilot instrument panel: a. Turbine Gas Temperature Indicator (TGT �C x 100). The TGT indicator is a dual, vertical-scale instru- ment with dual digital readouts beneath the scales. Tem- perature is sensed at the power turbine inlets by seven thermocouple probes. These signals are averaged and routed through the ECU/DECU, processed by the data signal converter, and transmitted to the crew station indi- cators. The DECU incorporates a 71 �C bias in its software which results in the indicated TGT reading cooler than the actual TGT. This permits use of the same TGT gauge for the -701 and -701C engines. When the helicop- ter is on battery power only and a given engine has not been started, the TGT signal is passed through the DECU to the TGT gauge without the 71 �C bias. When the heli- copter has 115 vac, 400 Hz power applied, and a given engine has not been started, the DECU is powered and applies the 71 �C bias to the TGT signal for display. If when the helicopter has 115 vac, 400 Hz power applied prior to starting a given engine and the actual TGT minus the 71 �C bias results in a negative number, the indicated TGT may be erroneous with a significant mismatch be- tween pilot and CPG TGT gauges. During engine start, the TGT will increase until the sum of the actual TGT mi- nus the 71 �C bias equals a positive number, then the indi- cated TGT values will be correct. b. Torque Indicator (TORQUE %). The torque indi- cator is a dual vertical-scale instrument with dual digital readouts beneath the scales. The engine torque sensor sends pulsed signals to the engine ECU/DECU where torque signals are computed and sent to the crew station indicators. Engine torque is also displayed in the flight symbology as a single value for both engines. The torque value represented indicates the highest engine torque of the two engines. If a greater than 12% torque split occurs between the engines, the displayed torque value will flash. At an engine torque value of 98% or greater, a box around the torque value will be present and begin to flash, indicating an impending continuous torque limit of 100%. The maximum displayed torque value is 120%. c. Gas Generator Turbine Speed Indicator (N_G RPM %). This is a dual, vertical-scale instrument with dual digital readouts beneath the scales. Speed signals are taken from the engine alternators and sent directly to the crew station indicators. d. Power Turbine and Main Rotor Speed Indicator (ENG-RTR RPM %). This is a triple, vertical-scale in- strument. The two outer scales (N_p 1 and N_p 2) indicate speeds of the power turbines. The engine power turbine driveshaft sensors transmit pulsed signals to the engine ECU/DECU where they are computed into speed signals and then sent to the crew station indicators. The middle scale registers main rotor speed (N_r) and receives inputs directly from a magnetic pickup-type tachometer genera- tor on the transmission. e. Oil Pressure Indicator (ENG OIL PSI x 10). This is a dual, vertical-scale instrument. Pressure signals are taken from the engine oil system transducers and are dis- played on the crew station indicators. 2.32.2 CPG Engine Instruments. The CPG instru- ment panel has a power turbine and main rotor speed ver- tical-scale indicator and an engine torque vertical-scale indicator identical to those on the pilot instrument panel. To compensate for the absence of TGT, N_G, and oil pres- sure indicators, a selectable digital display (SDD) panel (fig 2-21) is installed to the right of the CPG engine torque indicator. To obtain a readout, the SELECT knob is turned until an advisory light is displayed in the desired position on the right side of the panel. When the SELECT knob is rotated fully clockwise, no advisory light will be illuminated and the digital readout should be disregarded. Simulta- neously, left engine and right engine digital readouts ap- pear in the left upper corner of the panel for FWD and AFT