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 11.31.35
• If Altitude Intervention is used to initiate descent when more than 50
NM to T/D with VNAV engaged and the MCP ALT below current
altitude but at or above any descent constraint altitude, the result will be
a cruise altitude reset to the MCP ALT and Cruise Descent vertical
speed commands of -1000 fpm to the new cruise altitude.
• If Altitude Intervention is used to initiate descent when more than 50
NM to T/D with VNAV engaged and the MCP ALT below current
altitude and below a descent constraint altitude, the result will be Early
Descent vertical speed commands of -1000 fpm until path intercept or
MCP ALT level off occurs.
1 DES NOW (VNAV PTH)
With a VNAV path descent planned, VNAV starts an early descent at 1000 fpm
and captures the idle descent path. VNAV uses FMC SPD for the autothrottle
mode and VNAV PTH for the pitch mode.
2 DES NOW (VNAV SPD)
With a VNAV speed descent planned, VNAV starts an idle thrust early descent.
VNAV does not attempt to capture the VNAV descent path. VNAV uses VNAV
SPD for the pitch mode and the autothrottle commands IDLE, followed by ARM.
Approach
The FMC transitions to “on approach” when the airplane is within:
• 2 NM of the first approach waypoint (including approach transitions
such as arcs and procedure turns), or
• 2000 feet of airport elevation, whichever occurs first.
When the FMC is “on approach”, the following features are available:
• UNABLE RNP alerting levels are higher
• when preparing for a missed approach and the MCP altitude is set at
least 300 feet above the current airplane altitude, VNAV will continue to
command a descent
September 15, 2016
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