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
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 (NG
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 (Np 1 and Np 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 (Nr) 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, NG, 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