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Flight Management, Navigation -
Flight Management System
Operation
Cruise Climb
Setting an altitude above the current cruise altitude in the MCP altitude window
and pushing the altitude selector causes the cruise altitude to be set to the MCP
altitude and the airplane to climb to the new cruise altitude. The CRZ page
displays ACT ECON CRZ CLB.
Step Climb
Fuel and ETA predictions assume the airplane climbs at each predicted step climb
point as airplane weight decreases. FMC predicted step climb increments are
based on the step size shown on the CRZ page. Entering a step size of zero causes
the FMC to assume a constant altitude cruise.
Flight crew entry of a step altitude on the CRZ or RTE LEGS page overrides the
FMC step climb predictions. Entry of a step altitude on the RTE LEGS page
overrides a “Step To” entry made on the CRZ page.
Predicted step altitudes display on the RTE LEGS page. The distance andETA to
the next step point (predicted or flight crew entered) display on the CDU CRZ and
PROG pages. They also display on the ND map display with a green circle and
S/C label.
Cruise Descent
Setting an altitude below the current cruise altitude in the MCP altitude window
and pushing the altitude selector (more than 50 nm from a T/D) causes the cruise
altitude to be set to the MCP altitude and the airplane to descend to the new cruise
altitude. The CRZ page displays ACT ECON CRZ DES. If the altitude set in the
altitude window is below the speed transition (SPD TRANS) or restriction (SPD
RESTR) altitude displayed on the DES page, those altitudes and speeds are
deleted. Transition or speed restrictions must be maintained by flight crew action.
Descent
The FMC calculates a descent path based on airspeed and altitude constraints and
the end of descent (E/D) point. An E/D is created when an altitude constraint is
added to a waypoint in the descent phase. The altitude constraint can be entered
manually or may be part of a selected VFR or instrument approach procedure.The
E/D can be created at one of these positions:
• the final approach fix
• the outer marker (for some ILS approaches)
• the runway threshold for a VFR approach
• the runway threshold for a nonprecision approach with a runway
waypoint on the RTE LEGS page, or
• the missed approach point for a nonprecision approach not showing a
runway waypoint on the RTE LEGS page
Entering an arrival procedure provides an E/D.
October 1, 2000
747 Operations Manual
Flight Management, Navigation -
Flight Management System
Operation
Copyright © The Boeing Company. See title page for details.
D6-30151-425 11.31.23
The top of descent (T/D) point is calculated back the active route from the E/D. It
is the point where the cruise phase changes to the descent phase. The T/D displays
on the ND as a green circle with the label T/D.The descent path starts at the T/D
and includes waypoint altitude constraints. The path to the first constraint is based
on:
With theMCP altitude set below the current airplane altitude and at the T/D point,
the FMC commands idle thrust for the level deceleration segment and pitch to
track the descent path. Usually, the descent speed is economy above 10,000 feet
and 240 knots below 10,000 feet. Final deceleration is commanded to arrive at the
final approach fix or the outer marker at 170 knots.VNAVALT annunciates if the
airplane levels at anMCP altitude not in the FMC, or if the airplane passes the T/D
and the altitude window has not been set lower.
Target speeds are changed by entries on the LEGS or DESCENT pages. Forecast
descent winds and TAI/ON ALT for approach idle thrust may be entered on the
CDU FORECAST page.
If an unexpected (no entries on the DESCENT FORECASTS page) headwind
results in a significant reduction in airspeed to maintain path, thrust increases. The
FMS-CDU message THRUST REQUIRED displays if the A/T is disconnected
and thrust is required to maintain path. The FMS-CDU message DRAG
REQUIRED displays if an unexpected tailwind results in a significant increase in
airspeed to maintain path. If the airspeed deviation to maintain path is excessive,
the FMC directs the airplane to depart the descent path.
Approach
For VFR and nonprecision approaches displaying a runway waypoint on the RTE
LEGS page, the FMC calculated path is to a point 50 feet above the runway
threshold.
For a non–precision approach without a runway waypoint on the RTE LEGS page,
the VNAV path is calculated to the MDA or a calculated altitude at the missed
approach point. The calculated altitude may be below theMDA to ensure a flight
　
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