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or if the test fails, a fault code. Faults are classified as
either “HARD” or “SOFT”. In primary mode a hard fault
will cause the FADEC to transfer to Reversionary , while
in Reversionary a hard fault will cause the FADEC to “fail
fixed” to a constant power condition. If a hard fault occurs
in Primary after a hard fault exists in reversionary then
the primary will fail fixed. In the event of a soft fault the
FADEC will remain in the mode it was in prior to the fault
but there may be some degradation or redundancy. All
soft faults are less severe than a hard fault since the
FADEC will not switch modes due to a soft fault.
The activation of the BIT display is dependent upon the
position of the ECL as follows:
a. With the ECL at STOP, the fault information for
the last engine cycle and current faults are displayed.
b. When the ECL is positioned at GROUND only
current faults are displayed.
c. When the ECL is positioned at FLIGHT the display
will be turned off except as required for Power Assurance
Test (PAT).
2-3-35. Starting in Primary Mode. 714A
CAUTION
The (P3) compressor pressure signal line
going to the DECU contains a manually
operated moisture drain valve. This valve
shall not be drained while the engine is
running.
NOTE
Engine may not start if REV fail caution is
illuminated.
In primary mode, engine start is initiated with the ECL in
the GND position. Select and hold the respective ENG
START switch and allow the engine to accelerate to 10
TM 1-1520-240-10
2-3-10
Figure 2-3-7. DECU Panel 714A
percent N1 then release the ENG START switch. The
automatic start sequence has been energized and FADEC
will complete the start. When an engine start is
energized, FADEC turns on the engine start solenoid to
introduce fuel flow and energize the engine igniters. Successful
engine ignition is immediately indicated to FADEC
by an increase of PTIT or compressor speed (N1).
Engine temperature is monitored throughout the sequence
and will result in a fuel flow reduction if the temperature
exceeds 650C with a full cutback to minimum
flow limit at 760C. The starter motor and igniter are
automatically turned off when N1 speed exceeds 48 percent.
Ground idle is 50 to 59 percent and is corrected for
temperature. The engine is allowed to take 45 seconds
to stabilize at ground idle.
2-3-36. Engine Start Abort. 714A
PTIT above 816C will cause immediate fuel shutoff to
below minimum fuel flow. The ECL must be retarded to
STOP to achieve total fuel shutoff. A start abort results in
the ENG 1 (2) FAIL warning to be illuminated until the
abort is reset by moving the ECL to STOP.
2-3-37. Starting in Reversionary Mode. 714A
The initial start sequence in reversionary mode is the
same as in primary mode except, when N1 reaches 8
percent, the control system turns on the engine start fuel
solenoid to provide an initial altitude biased fuel flow and
activates the igniters and latches the starter motor. The
pilot can modulate fuel flow to the engine with ECL to
start the engine at a desired acceleration rate. Temperature
and temperature rate limiters are the same as in
primary mode except that the over temperature start
abort facility is not provided.
Alternate Reversionary Starting. For most conditions, a
start is successfully completed with the ECL held at the
GND position. However, if the engine fails to start due to
either a rich or lean hung start condition, the pilot may use
the ECL to increase or decrease the start flow as required
to complete a successful start.
a. Reversionary Rich Hung Start. A rich hung start
is characterized by N1 holding at about 40 percent and
PTIT climbing above 600C. If a rich hung start is experienced.
(1) Set the affected engine ECL to STOP.
(2) Allow PTIT to decay to 260C or below (motor
engine as required).
(3) Check N1 0 percent.
(4) Advance ECL half the distance between
STOP and GND (15).
(5) Motor engine using ENG START switch until
10% N1 and then release switch.
(6) After engine ignition (PTIT rising), slowly advance
ECL to GND. Check that N1 is stabilized at ground
idle.
b. Reversionary Lean Hung Start. A lean hung start
is characterized by N1 hanging approximately 30 percent
and PTIT remaining below 500C. If a lean hung start is
experienced.
(1) Slowly advance the hung engine ECL to
achieve acceleration (maximum of one-third travel from
GND to FLT).
(2) Retard the ECL to GROUND as ground idle
speed is approached. Check that N1 is stabilized at
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