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 11.31.27
Deceleration points show on the map as green open circles with the label DECEL.
Deceleration points show prior to:
• airspeed constrained waypoints
• holding patterns
• approach flap extension.
If more than one deceleration segment exists in the flight plan, only the next
deceleration point shows. Deceleration points can also show prior to cruise
holding patterns or other speed reductions.
During descent, VNAV ALT engages if the airplane levels at an MCP altitude not
in the FMC.
VNAV Path Descent
An E/D point must be defined in order to accomplish a path descent. It may be
defined manually or by the selection of an arrival procedure.
The FMC defaults to the path descent mode for planning purposes. If the
necessary information for a path descent is not available by the time the airplane
reaches the T/D point, the FMC will revert to the speed descent mode.
The path descent normally begins automatically at the calculated T/D point,
provided the MCP altitude is reset for the descent. If descent is not initiated by the
T/D, a path descent may not be achievable. At the T/D, the FMC commands idle
thrust and pitch to follow the descent path.
The descent complies with waypoint altitude restrictions by following the
calculated vertical path.
Note: A path descent uses the target speed for planning purposes only. There is
no attempt to maintain the target speed during the idle portion of the
descent.
YW273, YW274
(SB Changes YK981 - YQ456)
Note: When in path descent, if actual airplane speed is less than the descent target
speed by a customized threshold amount loaded in the Loadable Defaults
Database, the FMC will transition to FMC SPD as the thrust mode. The
valid range for the threshold is 5 to 15 knots. The A/T mode returns to the
retard/arm mode when the airplane speed is then equal to the target speed.
Note: When descending in VNAV PTH, the FCC will disengage VNAV and
switch to LVL CHG if actual speed becomes equal to or slightly less than
the minimum speed, denoted by the underspeed limiting symbol in the
MCP IAS/Mach window. This can also happen in turbulence or gusty
conditions when the minimum speed may momentarily increase due to G
loading. See section 4.20, Minimum Speed Reversion.
September 15, 2016
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