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CDE
ABOVE 18000'
CROSS
AT 6000'
BCD
CROSS
ABOVE 4000'
ABC
CROSS
UNABLE NEXT ALT
MESSAGE
10,000'
250 KTS
ECON CRZ SPD
T/C
WAYPOINT
CONSTRAINT
250 KTS
250 KTS
ECON CLB SPD
V2+10
ABC BCD
CDE
1
VNAV SPD
VNAV PTH
Acceleration height
VNAV active
VNAV SPD
VNAV PTH
3
4
2
5
(or VREF+100)
October 1, 2000
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
11.31.20 D6-30151-425
Flight Management, Navigation -
Flight Management System
Operation
1 Takeoff
When armed for takeoff, VNAV activates at 400 feet and pitch guidance continues
to maintain the target airspeed.
During takeoff, the FMC updates the target airspeed to the current airspeed until
VNAV activates. The target airspeed is between V2 + 10 and V2 + 25.
2 Acceleration Height
At acceleration height, flap retraction, or AFDS altitude capture below
acceleration height, VNAV commands an airspeed increase to the greater of 250
knots, VREF + 100 knots, or the speed transition associated with the origin airport,
limited by configuration.
The FMC changes the reference thrust limit to the armed climb thrust at the thrust
reduction point.
3 VNAV Climb
VNAV climb profile uses VNAV SPD or VNAV PTH at the default climb speed or
pilot selected climb speed to remain within all airspeed and altitude constraints
that are part of the SID entered into the active route. Autothrottle uses the armed
climb reference thrust limit.
If the climb speed profile cannot achieve an altitude constraint, the UNABLE
NEXT ALT scratchpad message displays.
4 Climb Constraints
VNAV enters the VNAV PTH mode to remain within departure or waypoint
constraints. Speed maintained during this time can be:
• procedure based speed restriction
• waypoint speed restriction
• default VNAV climb speed
• manually entered climb speed
If the FMC predicts the airplane will not reach an altitude constraint, the
FMS-CDU message UNABLE NEXT ALTITUDE displays. Speed intervention
can be used by pushing the IAS/MACH selector and manually setting a lower
arispeed to provide a steeper climb; or, climb derates can be deleted on the Thrust
Limit page.
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 11.31.21
5 Top Of Climb (T/C)
The point where climb phase meets the cruise altitude is called the top of climb.
Approaching this point, the FMC changes from climb phase to cruise phase. The
T/C displays any time the FMC calculates a change from climb phase to cruise
phase, such as step climb.
The T/C point displays on the map as a green circle with the label T/C.
MCP Altitude Intervention
Whenever the airplane levels 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 theMCP altitude 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 levels at FL250 in cruise.
Cruise
During cruise, the FMC commands economy cruise speed until reaching the
top–of–descent (T/D) point. Alternate cruise speed options are:
• long range (LRC)
• engine out (ENG OUT), or
• flight crew entered speed
The FMC commands maximum range cruise speed with the cost index set to zero.
Cost index modifications are allowed until within ten miles of the top of descent.
10,000'
FL250
T/C
VNAV ALT
Temporary Level Off
ECON CLB SPD
Altitude Selector Pushed
FL190
October 1, 2000
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
11.31.22 D6-30151-425
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波音747-441操作手册2(65)
