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rotor speed and high-pressure rotor speed are sensed by the
same dual-output sensors which drive the respective cockpitindicators
and are discussed in ENGINE INDICATING. Output signals from the
DEEC are directed to a torque motor in the fuel control unit and to the
control solenoids of the surge bleed control. The Ni DEEC utilizes an
additional pneumatic static pressure signal (PSO) to allow calculation
of airspeed (represented by Mach number). During engine start, the
DEEC provides automatic fuel enrichment up to 200° C PTT. Each
DEEC incorporates a built in test capability, which detects, stores and
annunciates faults. The Ni DEEC incorporates an Engine Condition
Trend Monitor (ECTM) function to provide operators with engine life
usage and condition trend information. Fault information and ECTM
data is accessed using a personal computer and application software
through a front panel mounted test connector, which supports an RS-
422 serial communications data bus. The N2 DEEC's built in test capability
displays fault codes in a window located on the DEEC's front
panel. A function select switch and calibration switch, located on the
N2 DEEC's front panel, allow for the adjustment of several operating
parameters, including fuel specific gravity adjustment. The fuel computers
operate on 28 VDC supplied through the 5-amp Land R FUEL
CMPTRcircuit breakers on the pilot's and copilot's circuit breaker panels
respectively.
FUEL CMPTR SWITCHES
The DEECs are controlled by two switches on the pilot's switch panel
labeled FUEL CMPTR L-MAN-OFF and R-MAN-OFF Normally, the
switches are left in theOn position.
2-4
PM-121
Change 4
Learjet 31A
Pilot's Manual
When the switch is OFF, the DEEC does notperform any engine control
functions. When the switch is On, the DEEC will automatically perform
the engine control functions listed above. When the switch is in the
MAN position, the DEECwill revert to the manual mode and not all engine
control functions will be available . The DEEC does provide engine
overspeed protection during manual mode operations.
FUEL CMPTR LIGHTS
SPR SWITCH
SURGE BLEED CONTROL
Illumination of either amber L or R FUEL CMPTR light on the annunciator
panel indicates a failure in or loss of power to the corresponding
DEEC. Circuits within the DEEC continuously monitor power supply,
computer circuits, and inputs to the computer. A loss of input power or
a computer malfunction will cause the monitor circuits to illuminate
the applicable FUEL CMPTR light and switch the DEEC to manual
mode. With the DEEC in the manual mode, cycling the applicable
FUEL CMPTR switch will reset the DEEC if the fault clears . If operating
in the manual mode, the DEEC will provide overspeed protection but
will not provide automatic mode functions. Also, the lights will be illuminated
whenever power is on the aircraft and the FUEL CMPTR
switches are in the OFF orMAN position.
The SPR (starting pressure regulator) switch is located on the pilot's
switch panel below the FUEL CMPTR switches. The switch has three
positions: L-Off-R. When the switch is positioned to L or R, the switch
commands the applicable DEEC to provide increased fuel scheduling
beyond the normal fuel enrichment schedule for engine start under
cold ambient conditions. Use of SPR is recommended for ground starts
when ambient temperature is below 0°F (-18°C) and for airstarts. SPR
should notbe used at ambient temperatures above 0°F (-18°C) and never
used at any time other than engine start. SPR is an DEEC function
and is inoperative with the DEEC off or in manual mode.
A surge bleed control system for each engine is installed to prevent
low-pressure compressor surge. Each system consists of two solenoid
control valves and a surge bleed valve. During normal operation, surge
bleed valve position is controlled by the DEEC via the solenoid control
valves. In the event a FUEL CMPTR light illuminates because of a failure
or the computer being switched to MANUAL or OFF, the surge
bleed valve will go to the 1/3-open position.
Pilot's Manual
Learjet 31A
FUEL HEATER (OPTIONAL)
Each engine may be equipped with a fuel heater which warms the
fuel to prevent ice formation on the engine fuel filter element. The
fuel heater is of a liquid-to-liquid design utilizing the engine lubricating
oil as a source of heat to warm the fuel. An anti-icing valve, in the
engine-driven fuel pump, monitors fuel temperature downstream of
the filter element and controls the flow of fuel into the oil-to-fuel heat
exchanger. The warm fuel exits the heat exchanger and mixes with
　
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