737 Flight Crew Operations Manual
Flight Management, Navigation -
Flight Management System
Operation
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 11.31.25
Descent
VNAV can perform a descent in either of two modes – path descent or speed
descent. During a path descent, the FMC uses idle thrust and pitch control to
maintain a vertical path, similar to a glideslope in three dimensions. During a
speed descent, the FMC uses idle thrust and pitch control to maintain a target
descent speed, similar to a level change descent.
Top Of Descent (T/D)
The point where the cruise phase changes to the descent phase is the top of
descent. The T/D point is shown on the map as a green open circle with the label
T/D. T/D is calculated from an end of descent (E/D) point.
Intermediate T/D points show on the map as green open circles with the label
T/D–XXXXX (altitude). Intermediate T/D points exist when path segments
between altitude restricted waypoints produce a level path segment. The
intermediate T/D point shows where the descent will resume.
YW273, YW274
(SB Changes YK981 - YQ456)
When an exit from a holding pattern is requested by the pilot through CDU action:
• a turn path to the inbound leg will be generated immediately if the
airplane is on the outbound leg or in the fix end turn when the T/D does
not occur in the hold pattern.
• the entire hold pattern will be flown when the T/D does occur in the
hold pattern.
End of Descent (E/D)
The FMC calculates a descent path based on airspeed restrictions, altitude
restrictions and the end of descent (E/D) point. The E/D point is shown on the map
as a green open circle with the label E/D. The E/D is the last of the following
which is not preceded by a lateral discontinuity:
(SB Changes YK981 - YQ456)
• the runway threshold for approaches with a runway waypoint on the
RTE LEGS page, or
YW273, YW274
(SB Changes YK981 - YQ456)
• the runway threshold for approaches with a runway waypoint on the
active RTE LEGS page, or
(SB Changes YK981 - YQ456)
• the missed approach point for approaches not showing a runway
waypoint on the RTE LEGS page, or
September 15, 2016
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