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operation, rpm, EGT, fuel flow, and nozzle position
vary with altitude and airspeed. The nozzle position
will also increase as the throttle is transitioned from
minimum AB to maximum AB. If an AB blowout
occurs, the autorelight feature attempts to reinitiate
AB without throttle movement. The engine has reduced
AB region of operation at high altitudes and
low airspeeds. The automatic AFT control feature,
rich stability cutback, reduces or limits the maximum
AB fuel flow in this region to prevent AB instabilities
(Figure 2-12). Indication of rich stability cutback is a
nozzle position of approximately 30 to 50 percent at
maximum AB rather than the normal 60 to 70 percent.
Also, because of airflow and temperature characteristics,
AB light-off characteristics are slower at
high altitudes and low airspeeds.
2.2.1.5 Secondary Mode. Basic engine operation
in SEC mode is extremely reliable. In the secondary
mode, the electronic functions performed by the AFTC
are eliminated. The MEC provides complete control of
the engine with the exception of fan speed limiting,
which is powered by the higher of 2%Vdc aircraft electrical
power or engine alternator electrical power. When
SEC mode is manually selected or an automatic default
to SEC mode occurs, the exhaust nozzle is commanded
full closed, the nozzle position indicator goes to the
not-powered position (subzero indication), the IGVs are
fixed full open, high-energy ignition is continuously
energized, AB is inhibited, and idle lockup protection is
lost.
In SEC mode, engine stall margin is decreaseda t low
‘pm because of IGV positioning. The FEMS engine
stall detection circuit is inoperative, but overtemperature
warning is still available. A low-level vibration/
rumble may be sensed in ground idle operation in
secondary mode. This vibration/rumble has no adverse
affect on the engine and disappearsw hen the throttle is
advanced slightly up to 5-percent rpm increase. Maximum
thrust available at military power in SEC mode is
depicted in Chapter 14, Figure 14-4.
SEC mode transfers with throttles in AB
above 450 KCAS could result in pop stalls
and damage to the IGV linkage.
Note
a SEC mode transfer from AB may result in
pop stalls. Nonemergency manual selection
of SEC mode on the ground should
be performed in basic engine. Nonemergency
manual selection of SEC mode airborne
should be performed in basic engine
with power set above 85-percent rpm.
a If the fan speed limiter circuit has failed,
engine rollback may occur with selection
of SEC mode. In the event of engine rollback,
PRI mode must be reselecteda bove
59-percentr pm or flameout will occur and
airstart will not he possible.
2.2.1.6 Engine Alternator. Each engine’selectrical
system is powered by an alternator mounted on the engine
afi gearbox. The alternator consists of four windings.
Two windings are redundant in providing power to
the AFTC and its components. A third winding provides
power for both main high-energy ignition and AB ignition.
The fourth winding provides power to the engine
monitoring system processor (for FEMS), and a signal
for the rpm gauge. The last winding is also an alternate
source of power for the fan speed limiting circuit. The
fan speed limiting circuit may be powered by either the
essential No. 2 dc bus or the engine-driven alternator
winding, depending on which source has the highest
stable output.
Ifengineahematorpoweroutputdropsbelowapreset
value, engine control will automatically transfer to SEC
mode, illuminating the respective engine SEC light. If
the engine reverts to SEC mode as a result of a sheared
alternator shaft, engine high-energy ignition will not be
available and the engine SEC light will not illuminate..
Cockpit indications will be loss ofenginerpmand nozzle
position indicating below zero. In failure modes, redundant
aircraft electrical power will be available for fan
overspeed protection.
The engine is completely operable should the aircraft
experience a complete electrical failure. The engine
operates in either PRI or SEC mode, which can be
selected automatically or manually. In case of a complete
electrical failure all engine lights and indicators
are inoperative.
ORIGINAL 2-14
NAVAIR WIWAAD1
RICH STABILITY CUTBACK
Figure 2-12. Rich Stability Cutback - F1 IO-GE400 Engine
2-15 ORIGINAL
NAVAIR Of-Fl4AAD1
2.2.1.7 Turbine Blade Temperature (Pyrometer).
The pyrometer is a fuel-cooled, photodiode, optical
unit that measures infrared radiation from the metal
　
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