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It consists of an impending bypass indicator, a filter ESC electronically controls engine operation by
element and a filter bypass valve. The filter can be evaluating the following discrete inputs: power turbine
seen by opening the left engine access door (11, fig. 2- trim switch selection, NG speed, NP speed, TGT,
1). collective position, pressure altitude, and outside air
( 1 ) Impending Bypass I n d i c a t o r . The temperature. The ESC uses these inputs during start
impending bypass indicator is a red button that extends and above 96% NP to control NG RPM with the PY
when an impending bypass condition exists. Notify torquemotor to vary PY air pressure against PX air
maintenance personnel if indicator extends. pressure in the bellows/fuel metering valve assembly in
the fuel control unit (FCU). The ESC operates in the
(2) Filter Element. The filter element is a 10 digital or analog mode. Both modes maintain a constant
micron, disposable filter element. power turbine speed (NP) and provide overspeed
2-25
TM 1-1520-248-10
protection. The ESC is programmed to continually with a high gross weight/density altitude
perform tests of its internal condition and the integrity will cause transients to the extent that
of incoming signals. If a fault is detected which causes the low rotor/high rotor warning message
degraded operation of the ESC digital mode, an may be activated; therefore, maneuvers
advisory message of FUEL CONTROL displays on the that require OGE capability should not be
MFD. Failures that will activate the FUEL CONTROL performed. Crews must monitor NR/NP/
advisory message are: loss of a single NG or NP NG to ensure that they remain within
monopole signal (the monopole pickups are dual type normal operating limits.
pickups with two independent coils and each provides
an RPM signal), loss of the TGT signal, loss of (2) Analog Mode. The analog mode is the
collective pitch position signal, open or short circuit in backup mode of operation for the ESC. The analog
the overspeed dump solenoid, and miscellaneous mode can be selected manually. This is done by
internal failures. The FUEL CONTROL advisory placing the NORM ANLG BACK UP switch to the ANLG
message will also appear during interrogation of the BACK UP position. This removes power from the digital
digital mode of the ESC. The FUEL CONT caution side of the ESC. There is no indication to the pilot the
message indicates to the pilot that the ESC has analog mode has failed. Therefore, caution should be
switched from the digital (primary) to the analog used when first selecting the analog mode. When
(backup) mode. A FUEL CONTROL advisory message operating in the analog mode, the following functions
will also appear. Failures that can activate a FUEL are not available: engine start temperature limiting, NP
lCoOssN Tof cbaouthtio NnG m seisgsnaaglse oarr eb:o tlho sNsP o sf ig2n8a lVsd, ca tsoh oErSt Cor, trim control, NP acceleration protection, and collective
open circuit to the PY torquemotor, loss of collective anticipation. In the analog mode, NP overspeed trips at
pitch and ambient pressure input simultaneously, and 113% and is not rate sensitive.
internal failure of the digital mode of the ESC. Faults of
the digital mode of the ESC can occur without the NOTE
corresponding caution or advisory messages. All fault
codes are held in memory and can be accessed by Both d i g i t a l and a n a l o g overspeed
interrogating the ESC. The ESC does not have a protection is active when operating in the
continuous memory; therefore, once electrical power to digital mode.
twhiell dbieg itloasl tm. oCdirec uoift tphreo tEecStCio nis isre pmroovveidde,d a bll yf atuhlet cFoUdEeLs (3) Manual Mode. The manual mode is used in
CONTR analog and FUEL CONTR DIGT circuit the event of a digital and analog failure or a total loss
breakers located in the forward overhead console panel of electrical power to the ESC. NP speed and power
(fig. 2-8). If both modes of the ESC fail, the engine can adjustments are controlled by throttle inputs.
be controlled manually through the use of the throttle. c. Fuel Control Panel. The fuel control panel (item
(1) Digital Mode. The digital mode is the 13, fig. 2-6., and fig. 2-13) is located on the right side
normal mode of operation for the ESC. The mode of the center pedestal. It contains a covered NORM
provides for: engine start temperature limiting, NG ANLG BACK UP switch and two push type switches
speed governing, NG acceleration control, NG labeled DIGITAL and ANALOG.
overspeed protection, NP speed governing, NP trim
control, NP acceleration protection, NP overspeed NOTE
protection, and collective anticipation. In the digital
mode, NP overspeed protection will trip at 122% and is
rate sensitive. This value is reset lower if NP RPM is • Any interruption in DC power will erase
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TECHNICAL MANUAL OPERATOR’S MANUAL FOR ARMY OH-58D HELICOPT(12)
