787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Flight Management, Navigation -
Flight Management System
Operation
Copyright © The Boeing Company. See title page for details.
11.31.26 D615Z003-TBC
If flight plan modifications or unknown winds occur when below 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 10 knots less than the transition speed for the
destination airport (not less than minimum maneuvering speed), and the
CDU help window message THRUST REQUIRED displays again.With
autothrottles active, this condition should not occur as thrust levers are in
SPD and target speed is maintained during the descent
• with greater than 10 knots above target speed, the CDU help window
message DRAG REQUIRED displays. The airplane may accelerate up to
15 knots above target speed to maintain the path. The maximum speed
excursion allowed is 5 knots above the transition speed after the airplane is
below transition altitude for the destination airport or 5 knots below the
flaps placard speed if flaps are extended. If further correction is required,
VNAV may allow the airplane to rise up to 150 feet above the path to stop
the acceleration. 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
commands a speed 10 knots less than the transition speed for the
destination airport, and the CDU help message DRAG REQUIRED
displays again
Early Descent
When a descent is started before the T/D, VNAV commands a descent at a reduced
descent rate until the descent path is intercepted.
Start an early descent by selecting the DES NOW prompt on the DES page or by
pushing the MCP altitude selector. In an early descent, the autothrottle mode
annunciation is initially THR, followed by HOLD, allowing the pilot to adjust the
rate of descent. The pitch mode is VNAV SPD.
August 14, 2009
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