737 Flight Crew Operations Manual
Engines, APU -
Engine System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
7.20.10 D6-27370-866-EGP
Engine Start System
Starter operation requires pressurized air and electrical power. Air from the bleed
air system powers the starter motor. The APU, an external ground cart, or the other
operating engine provides the bleed air source.
In the GRD position, the engine start switch uses battery power to close the engine
bleed air valve and open the start valve to allow pressure to rotate the starter. When
the start valve opens, an amber START VALVE OPEN alert is provided on the
upper display unit. The starter rotates the N2 compressor through the accessory
drive gear system. When the engine accelerates to the recommended value (25%
N2 or max motoring), moving the engine start lever to the IDLE position opens
the fuel valves on the wing spar and engine, and causes the EEC to supply fuel and
ignition to the combustor where the fuel ignites. Initial fuel flow indications lag
actual fuel flow by approximately two seconds, therefore, during engine start, an
EGT rise may occur before fuel flow indication.
At starter cutout speed (approximately 56% N2), power is removed from the start
switch holding solenoid. The engine start switch returns to OFF, the engine bleed
air valve returns to the selected position, and the start valve closes.
Abnormal Start Protection (Ground Starts Only)
During ground starts, the EEC monitors engine parameters to detect impending
hot starts, engine stalls, EGT start limit exceedances, and wet starts. These
protection features do not function during inflight starts.
If an impending hot start is detected by a rapid rise in EGT or EGT approaching
the start limit, or a compressor stall occurs, the white box surrounding the EGT
digital readout flashes white. The flashing white box resets when the start lever is
moved to CUTOFF or the engine reaches idle N2. Current versions of EEC
software (7.B.Q and later) automatically turn off the ignition and shuts off fuel to
the engine for an impending hot start or stall.
If the EGT exceeds the starting limit, the EGT display, both box and dial, turn red.
The EEC automatically turns off the ignition and shuts off fuel to the engine. The
alert terminates and the display returns to white when EGT drops below the start
limit. Following shutdown of both engines, the EGT box turns red to remind the
crew of the exceedance.
A wet start occurs if the EGT does not rise after the start lever is moved to IDLE.
If a wet start is detected, the EEC turns off the ignition and shuts off fuel to the
engine 15 seconds after the start lever is moved to IDLE.
September 26, 2013
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