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temperature exceeds limits. The system will motor the
starter for up to 60 seconds or until TGT is below 149
°C (300 °F), whichever occurs first. These features are
not available in the manual mode.
It is critical for the pilot to monitor engine parameters
during starting even though the FADEC system has hot
start abort logic. If an incorrect maintenance procedure
is used, the ECU may fail because it is unable to
reduce fuel flow to the scheduled value. Hot start abort
logic is not available with a FADEC fail condition. If no
action is taken, the engine can hot start.
406530-48
J0863
Figure 2-14. AUTO/MAN switch (6) Limit Override Logic. The FADEC system
provides automatic limiting functions including
CAUTION temperature limiting, torque limiting, NG speed limiting,
and NP overspeed protection when operated in the
automatic mode. The FADEC system incorporates logic
To p r e v e n t u n c o n t r o l l a b l e r o t o r to automatically override engine threshold operating
overspeed and damage to drive train limits based on the engine operating condition and
components while on the ground, do not when main rotor speed droop exceeds 7%.
switch to manual mode unless the (7) NG Governing System. The FADEC system
collective is full down and the throttle is interfaces with the engine NG monopole speed sensor
at idle. to measure gas producer turbine speed. The FADEC
(4) Mode Switching. Mode switching is done by system adjusts the engine acceleration schedule based
pressing the FADEC AUTO/MAN switch (21, fig. 2-6) on NG speed, ambient temperature, and pressure.
and confirming that the desired legend is illuminated. Temperature input is provided by the CIT probe
The switch incorporates a spring released latching mounted in the particle separator near the compressor
mechanism. Switching from the manual to automatic inlet. Ambient pressure input is provided by a
mode reinitiates fault detection and clears all current transducer in the ECU. Fuel flow is scheduled as
faults from ECU volatile memory (RAM). Non-volatile required to satisfy power demand. The NG mechanical
ECU memory is unaffected. Fault codes displayed by threshold limit is 105%. The NG mechanical override
the CDS are also unaffected. These codes are limit is 106%. This feature is not available in the
permanently latched and are not cleared until the manual mode.
engine monitor page reset code is input from the (8) NP Governing System. The FADEC system
keyboard unit. interfaces with the engine NP monopole speed sensor
to measure power turbine speed and provide power
CAUTION turbine overspeed protection. The FADEC system
governs power turbine speed (NP) in the normal
operating range from 95% to 105% NR using the NP
To prevent a hot start it is critical to trim switch mounted on the pilot collective control head.
visually confirm that the correct legend The FADEC system receives a discrete rotor speed
is illuminated on the AUTO/MAN switch. input signal from a rotor speed sensor located on the
2-29
TM 1-1520-248-10
right aft transmission housing. This feature is not (14) Fault Monitoring. The FADEC system
available in the manual mode. incorporates logic and circuitry to perform self
diagnostics.
(9) Overspeed System. The FADEC system
incorporates an analog NP overspeed control system An automatic FADEC power up check exercises all
that is designed to provide overspeed protection due to electrical circuitry to assure system functionality and
loss of load events (shaft failures). The NP overspeed readiness.
system is activated at 124% NP and operational in both
the automatic and manual modes. b . E n g i n e F u e l S y s t e m E l e c t r i c a l
Components. The electrical components of the engine
( 1 0 ) TGT System. The FADEC system fuel system are the ECU, AUTO/MAN switch, power
continuously monitors engine TGT to prevent steady turbine rpm trim control, ignition system, Ng and Np
state or transient temperature limit exceedances. The monopole pickup units, turbine gas temperature (TGT)
FADEC system reduces fuel flow to prevent an measurement components, and Np overspeed solenoid.
exceedance. The TGT run threshold limit is 815 °C
(1499 °F). The TGT run override limit is 1093 °C (1999 c. 10-Micron Fuel Filter. The fuel filter is mounted
°F). These features are not available in the manual on the lower rear portion of the power and accessory
mode. gearbox and is driven by the gas producer turbine. it
consists of an impending bypass indicator, a filter
(11) Torque System. Torquemeter oil pressure element, and a filter bypass valve. The filter can be
is measured by a sensor connected to the engine seen by opening the left engine access door (11, fig. 2-
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TECHNICAL MANUAL OPERATOR’S MANUAL FOR ARMY OH-58D HELICOPT(15)
