DEEC begins the auto-start sequence by en-
ergizing the standby fuel pump for that engine,
and energizing the start relay (line contactor)
through the GCU (generator control unit). The
starter drives the tower shaft through the ac-
cessory gearbox, which in turn, drives the N
2
spool.
The DEEC commands ignition at 6.8% N
2
causing the green IGN annunciator to illumi-
nate on the EICAS. Fuel is introduced when
positive N1 is sensed by the DEEC at ap-
proximately 11-12% N2. The DEEC precisely
regulates fuel flow and engine acceleration
during start. It provides automatic enrichment
to provide a smooth acceleration to idle speed.
At approximately 50% N2 (dependent on am-
bient conditions), ignition is terminated and
the speed sensor in the starter/generator trips
to disengage the starter relay (line contactor).
As a follow-up, the DEEC will also signal
starter relay disengagement at 50% N2. If a
GPU is not being used, a signal from the DEEC
will automatically bring the generator on line
when the engine RPM is at 95% of N1 ground
idle. If the DEEC is not operating in the au-
tomatic mode, the GEN S/I must be depressed
to turn the generator on.
The automatic start sequence is generally very
reliable and trouble free; however, the pilot
should carefully monitor the N1 and N2 spools,
ITT and oil pressure during start. If both spools
do not increase smoothly and rapidly to idle
rpm after light-off, then the start should be
aborted. The maximum time for the engine to
accelerate from initiation of start to idle N1
is 60 seconds.
If an indication of ITT has not occurred within
10 seconds after start initiation or ITT is ap-
proaching the limit and climbing rapidly, the
start should be aborted.
An indication of oil pressure should occur
within 10 seconds of light-off. If no oil pres-
sure is indicated the start should be aborted.
The engine can be started in the manual mode
also, but the precise fuel scheduling, fuel en-
richment, temperature and rpm limiting, and
automatic control of the start, standby fuel
pump and ignition are not provided.
There is no Airplane Flight Manual proce-
dure for starting an engine on the ground with-
out the DEEC ON. There is, however, a
checklist for doing an airborne start with the
DEEC selected to MAN or OFF.
LEARJET 45 PILOT TRAINING MANUAL
7-26
FOR TRAINING PURPOSES ONLY
FlightSafety
international
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