737 MAX Flight Crew Operations Manual
Flight Management, Navigation -
Flight Management System
Operation
11.31.30
MN-FLT-OH-201
If a path (VNAV PTH) descent is active when a vertical angle leg becomes active,
the path mode will remain active, but VNAV will follow the vertical angle rather
than the idle thrust descent path.
Early Descent
When in VNAV ACT DES, the FMC is considered to be in early descent when the
airplane is below the computed descent path. VNAV commands a 1000 fpm
descent until the idle descent path is intercepted or an FMC target altitude is
complied with for any AT, or At-or-Above altitude constraints that exists in the
flight plan, whichever occurs first i.e. idle descent path intercept or FMC target
altitude compliance.
To start an early descent, use DES NOW prompt on the DES page.
A CRZ DES occurs when lowering the MCP ALT to a lower altitude, but at or
above any descent constraint altitude and pressing ALT INTV if the airplane is
further than 50 nm from the top of descent at the current cruise altitude. If within
50 nm of the top of descent, the Early Descent mode will be invoked.
• A cruise descent can be started by using the altitude intervention feature
on the MCP when the airplane is not within a distance of 50 NM to the
T/D, or by entering a new cruise altitude on the FMC CRZ page after
setting the new level-off altitude in the MCP.
• Altitude Intervention may be used to initiate early descent when the
airplane is 50 nm or less to Top of Descent.
• If Altitude Intervention is used to initiate descent when 50 NM or less to
T/D and the MCP ALT below current altitude, or descent is initiated via
DES NOW prompt on the DES page, Early Descent vertical speed
commands of -1000 fpm are generated by the FMC for autopilot V/S
tracking until path intercept, or next constraint altitude if altitude is
reached when VNAV is engaged, or MCP ALT level off occurs.
• 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.
March 1, 2021
