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DES
APPROACH
CLB
VNAV PTH
VNAV SPD
ALTITUDE
VNAV PTH
RESTRICTION
VNAV PTH
VNAV SPD
CLB
ALTITUDE
VNAV PTH
RESTRICTION
DES
VNAV SPD
o T/D
SPEED INTERVENTION PITCH MODES
787 Flight Crew Operations Manual
Flight Management, Navigation -
Flight Management System
Operation
11.31.22 Boeing Proprietary
During a VNAV, non-ILS approach while using speed intervention, the pitch mode
is VNAV PTH. The vertical path is maintained regardless of IAS MACH selector
changes.
If a “direct to” is executed to a waypoint in the approach, VNAV transitions to the
approach phase when the airplane passes the “direct to” waypoint. If a waypoint
located after the first waypoint of an FMC database approach is added and
executed, VNAV will not transition to approach phase when passing the first
waypoint of the approach.
Descent
The FMC calculates a descent path based on airspeed and altitude constraints and
the end of descent (E/D) point. Dashes display on the LEGS page for speed and
altitude descent waypoints. When an arrival or approach procedure is selected on
the ARRIVALS page and incorporated into the flight plan, the FMC creates an
E/D. The E/D is located 50 feet above the runway threshold (RW waypoint) for all
approaches except VOR approaches. The E/D for VOR approaches is the missed
approach point; which may be the VOR, runway waypoint (RWXXX), or a named
waypoint. During cruise, an E/D is also created when an altitude constraint is
entered on the LEGS page on a downstream waypoint.
The top of descent (T/D) is the point where the cruise phase changes to the descent
phase. It 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:
The descent may be planned at economy Mach/CAS (based on Cost Index) or a
manually entered Mach/CAS. VNAV will not command an economy target speed
greater than (VMO/MMO minus 16 knots) or a pilot entered speed greater than
(VMO/MMO minus 11 knots).
The FMC creates the descent path with a deceleration at the speed transition
altitude (typically 250 knots below 10,000 feet). VNAV plans a speed target 10
knots below the transition speed to allow for unknown tailwinds.
Descent path segments after the first altitude constraint waypoint are constructed
as straight line point-to-point segments. If the VNAV path segment is too shallow
to be flown satisfactorily at IDLE thrust, the FMC commands speed on thrust
levers (SPD). Elevators control the shallow descent path.
• speedbrakes retracted
• FMC cruise wind
• applicable target speed
• wind entries on the DESCENT
FORECAST page
• predicted use of anti-ice
787 Flight Crew Operations Manual
Flight Management, Navigation -
Flight Management System
Operation
Boeing Proprietary 11.31.23
If flight plan modifications or unknown winds occur when above the first speed
constraint, VNAV continues to maintain the path and allows the speed to vary up
to the following limits:
• with greater than 15 knots below the target speed, and autothrottles not
active, the CDU help window message THRUST REQUIRED displays.
The airspeed may decrease to minimum maneuvering speed.
Subsequently, VNAV commands the airplane to fly below the path to stop
the deceleration. If VNAV can no longer maintain the airplane within 150
feet of the path without further deceleration, speed reversion occurs, the
pitch mode annunciation changes from VNAV PTH to VNAV SPD,
VNAV resets the target speed to 5 knots above the greater of best holding
speed or minimum maneuvering speed, and the CDU help window
message THRUST REQUIRED displays again. With autothrottles active,
this condition should not occur as throttles are in SPD and target speed is
maintained during the descent
• with greater than (VMO/MMO minus 16 knots), the CDU help window
message DRAG REQUIRED displays. The airplane may accelerate up to
(VMO/MMO minus 11 knots) to maintain the path. If further correction is
required, VNAV may allow the airplane to rise up to 150 feet above the
path. If VNAV can no longer maintain the airplane within 150 feet of the
path without further acceleration, speed reversion occurs, the pitch mode
annunciation changes from VNAV PTH to VNAV SPD, VNAV resets the
target speed to (VMO/MMO minus 16 knots), and the CDU help window
message DRAG REQUIRED displays again. The speed tape will display
a VNAV PTH speed band during descent.
787 Flight Crew Operations Manual
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787机组操作手册Flight Crew Operations Manual 3(30)
