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Alternate mode provides equal or greater thrust than normal mode for the same
Thrust lever position. Thrust does not change when EEC transfers control from
normal mode to alternate mode. Thrust increases when alternate mode is selected
manually. When thrust is greater than idle, the Thrust lever should be moved aft
prior to manually selecting alternate mode so thrust does not exceed maximum
N1.
December 01, 1999
747 Operations Manual
Engines, APU -
Engine System Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 7.20.5
If control for any EEC transfers from normal to alternate, the autothrottle
disconnects. The autothrottle can be activated after all EECs are manually
transferred to alternate mode.
EEC Idle Selection
The EEC selects minimum idle or approach idle. Minimum idle is a lower thrust
than approach idle. Approach idle is selected in flight when:
• nacelle anti–ice is ON
• flaps are in landing position
• Continuous Ignition switch is ON
• during thrust reverser operation
Approach idle decreases acceleration time for go–around. Approach idle is
maintained until five seconds after touchdown, when minimum idle is selected.
EEC Overspeed Protection
At thrust settings above idle, the EEC monitors N1 and N2 RPM to prevent rotor
overspeed. If a rotor approaches overspeed, the EEC commands the fuel metering
unit to reduce fuel flow to keep rotor speed from exceeding the operating limit
even though the Thrust lever is commanding more thrust.
October 1, 2000
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
7.20.6 D6-30151-425
Engines, APU -
Engine System Description
Engine Start and Ignition System
The engines can be started using the autostart system or manually. Autostart is the
normal starting mode. During autostart, the EEC sequences start valve, engine fuel
valve, and igniter operation. Selecting OFF on the Autostart switch disables
autostart and allows manual, pilot–monitored, starting. During manual start, the
flight crew sequences the operation of the start valve, engine fuel valve, and the
selected igniter.
Air from the bleed air duct powers the starter motor, which is connected to the N2
rotor. The starter air source is normally the APU, but air from ground carts or
another running engine can be used.
Start Indications
Start indicators display with engine indications when an engine is shutdown. A
start limit displays on the EGT indication when the Fuel Control switch is in
CUTOFF. It remains displayed until the engine stabilizes at idle. The EGT
indication changes color to red if the EGT start limit is reached. A fuel-on
indicator displays on the N2 indication when the Fuel Control switch is in
CUTOFF. The fuel-on indicator displays the minimum N2 RPMat which the Fuel
Control switch should be moved from CUTOFF to RUN.
An in-flight start envelope displays on primary EICAS and the secondary engine
indications display when a Fuel Control switch is moved to CUTOFF in flight.
The in-flight start envelope displays the airspeed range to ensure an in-flight at the
current flight level. If the current flight level is greater than the maximum start
altitude, the maximum start altitude and related airspeed range display. X-BLD
displays next to the N2 indication if crossbleed air is necessary for start.
Autostart
Autostart allows the EEC to control fuel and ignition and automatically abort the
start for certain malfunctions. Pushing the Autostart switch ON arms autostart.
Pulling the Start switch out (held out by a solenoid) arms the start valve and opens
the engine bleed air valve. Moving the Fuel Control switch to RUN initiates the
autostart sequence.
The EEC opens the start valve and the Start light illuminates. At a predetermined
N2, the EEC opens the fuel metering valve and energizes the selected igniter. One
igniter is normally selected for ground start, while two igniters are selected for
in-flight start.
Starter cutout occurs at 50% N2 RPM. At starter cutout, the Start switch is
released to the in position, the start and engine bleed air valves close, the Start light
extinguishes, and ignition discontinues.
October 1, 2000
747 Operations Manual
Engines, APU -
Engine System Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 7.20.7
During autostart, the EEC monitors EGT and N2 RPM until the engine stabilizes
at idle.
Ground Autostart
During ground start, the autostart system monitors engine parameters and aborts
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