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• default VNAV climb speed
• manually entered climb speed
If the FMC predicts the airplane will not reach an altitude constraint, the
FMS–CDU help window message UNABLE NEXT ALTITUDE displays. Speed
intervention can be used by pushing the IAS/MACH selector and manually setting
a lower airspeed to provide a steeper climb; or, climb derates can be deleted on the
THRUST LIMIT page.
The point where the climb phase meets the cruise altitude is called the top of
climb. Approaching this point, the FMC changes from the climb phase to the
cruise phase. The T/C displays any time the FMC calculates a change from a climb
phase to a cruise phase, such as a step climb.
The T/C point displays on the map as a green open circle with the label T/C.
2 Acceleration Height
3 VNAV Climb
4 Climb Constraints
5 Top Of Climb (T/C)
787 Flight Crew Operations Manual
Flight Management, Navigation -
Flight Management System
Operation
11.31.20 Boeing Proprietary
MCP Altitude Intervention
Whenever the airplane levels off at an MCP altitude not in the FMC, VNAV ALT
annunciates. For example, FMC cruise altitude is FL250 and the clearance
altitude, FL190, is set in the MCP. Pitch maintains altitude and thrust maintains
FMC target speed. In the example, the speed after the temporary level off would
be ECON CLB SPEED.
Setting the clearance altitude in the MCP window and pushing the altitude selector
continues the climb. VNAV SPD activates. Pitch maintains FMC speed and thrust
increases to the armed reference thrust limit. In the example, the airplane climbs
to FMC CRZ ALT and then levels at FL250 in cruise.
Cruise
During cruise, the FMC commands economy cruise speed or the pilot entered
speed until reaching the top–of–descent (T/D) point. Other cruise speed options
are:
• long range (LRC)
• engine out (ENG OUT)
• flight crew entered speed
• flight crew entered constant Mach between two or more waypoints
• required time of arrival (RTA)
The FMC commands maximum range cruise speed with the cost index set to zero.
Cost index modifications are allowed until passing the top of descent.
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.
10,000'
T/C
ECON CLB
FL190
TEMPORARY
LEVEL OFF
VNAV ALT
ALTITUDE
SELECTOR
PUSHED
FL250
SPD
787 Flight Crew Operations Manual
Flight Management, Navigation -
Flight Management System
Operation
Boeing Proprietary 11.31.21
Flight crew entry of a step altitude on the CRZ or RTE LEGS page overrides the
FMC step climb predictions for the next predicted step. Once a step climb to that
altitude is predicted, the FMC resumes normal step altitude prediction. Entry of a
planned 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 and ETA to
the next step point (predicted or flight crew entered) display on the CRZ and
Progress 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.
MCP Speed Intervention
With VNAV active, pushing the IAS MACH selector enables speed intervention.
Speed intervention allows the flight crew to change airplane speed with the
IAS/MACH selector.
The above illustration shows the VNAV pitch flight mode annunciation for each
phase of flight when using speed intervention.
In a VNAV descent after the T/D, VNAV PTH changes to VNAV SPD during
speed intervention. In all other phases, the pitch mode does not change with speed
intervention. Pitch controls speed in VNAV SPD mode, and during the VNAV
PTH descent prior to speed intervention. Otherwise, thrust controls speed in
VNAV PTH mode.
VNAV SPD
CRZ
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787机组操作手册Flight Crew Operations Manual 3(29)
