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Engines, APU -
Engine System Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 7.20.3
Compact Display Format
If only one CRT is available for use by EICAS, primary EICAS always displays.
Primary engine indications display in the normal format. Secondary engine
indications are selected by pushing the Secondary Engine Display switch. Pushing
the switch displays the primary and secondary engine indications on primary
EICAS in compact format. In compact format, N1 displays by digital and vertical
indicators while all other engine indications display by digital indicators. Pushing
the switch again removes the secondary engine indications and returns the primary
engine indications to normal format.
Partial Display Format
Secondary engine indications display in partial format if a secondary engine
parameter exceeds the normal operating range when the secondary engine display
is not selected. The secondary engine exceedance cue displays on primary EICAS
when an exceedance occurs.
If an N2 RPMincreases to the operating limit, the N2 indications display. If an oil
pressure decreases or an oil temperature increases to the caution range or
operating limit, or if an oil quantity decreases to the low level, or the oil quantity
differential is exceeded, the oil indications display. If an engine vibration increases
to the display indicator, the vibration indications display.
Pushing the Secondary Engine Display switch while the secondary engine display
is in the partial format displays the entire secondary engine display. Pushing the
switch again returns the secondary engine display to partial format.
Selecting another secondary EICAS display while the secondary engine display is
in partial format removes the secondary engine display from secondary EICAS.
The partial secondary engine indications display with the primary engine
indications on primary EICAS in compact format.
If only one CRT is available for use by EICAS and a secondary engine parameter
exceedance occurs, the primary and partial secondary engine indications display
on primary EICAS in compact format.
If the secondary engine exceedance cue displays and partial secondary engine
indications are not displayed, pushing the Status Display switch displays the
primary and partial secondary engine indications on primary EICAS in compact
format.
In all cases, the partial secondary engine indications and secondary engine
exceedance cue remain displayed until the exceeding engine parameter returns to
the normal operating range.
December 01, 1999
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
7.20.4 D6-30151-425
Engines, APU -
Engine System Description
Electronic Engine Control (EEC)
Each EEC has full authority over engine operation. The EEC uses Thrust lever
inputs to control forward and reverse thrust. The EEC has two control modes:
normal and alternate. In both normal and alternate modes, the EEC uses N1 RPM
as the controlling parameter for setting thrust.
The EEC calculates an N1 value between idle and maximum N1.Maximum N1 is
the maximum allowable thrust available from the engine. The calculated N1 is
compared to actual N1 RPM. The EEC commands the fuel metering unit to adjust
fuel flow until actual N1 equals calculated N1.
EEC Normal Mode
In normal mode, EEC sets thrust by controlling N1 based on Thrust lever position.
N1 is commanded by positioning the Thrust levers either with the autothrottles, or
by the flight crew.
When the engine is stabilized, EEC keeps thrust constant independent of outside
air temperature and pressure. The EEC adjusts thrust for changes in nacelle and
wing anti-ice and airplane pressurization bleed requirements. This allows a fixed
Thrust lever position throughout a climb.
Maximum N1 represents the maximum rated thrust available from the engine. The
EEC continuously computes maximum N1. Thrust is limited to maximum N1 at
the full forward Thrust lever position. Maximum thrust is available during any
phase of flight by moving the Thrust lever to the full forward position.
EEC Alternate Mode
The EEC uses alternate mode as a backup to normal mode. If EEC detects a fault
and can no longer control the engine using the normal mode, it transfers control to
alternate mode. Alternate mode can also be selected manually using the EEC
Mode switch.
Alternate mode does not provide thrust limiting at maximum N1.Maximum N1 is
reached at a Thrust lever position less than full forward. Thrust levers must be
adjusted to maintain desired thrust as environmental conditions and bleed
requirements change.
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