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.
11.31.24 D615Z003-TBC
During a VNAV, non-ILS approach while using speed intervention, the pitch mode
is VNAV PTH. The vertical path is maintained regardless of IAS MACH selector
changes.
If a “direct to” is executed to a waypoint in the approach, VNAV transitions to the
approach phase when the airplane passes the “direct to” waypoint. If a waypoint
located after the first waypoint of an FMC database approach is added and
executed, VNAV does not transition to approach phase when passing the first
waypoint of the approach.
Descent
The FMC calculates a descent path based on airspeed and altitude constraints and
the end of descent (E/D) point. Dashes display on the LEGS page for speed and
altitude descent waypoints. When an arrival or approach procedure is selected on
the ARRIVALS page and incorporated into the flight plan, the FMC creates an
E/D. The E/D is located 50 feet above the runway threshold (RW waypoint) for all
approaches except VOR approaches. The E/D for VOR approaches is the missed
approach point; which may be the VOR, runway waypoint (RWXXX), or a named
waypoint. During cruise, an E/D is also created when an altitude constraint is
entered on the LEGS page on a downstream waypoint.
The top of descent (T/D) is the point where the cruise phase changes to the descent
phase. It displays on the ND as a green circle with the label T/D. The descent path
starts at the T/D and includes waypoint altitude constraints. The path to the first
constraint is based on:
• off-idle thrust
• speedbrakes retracted
• FMC cruise wind
• applicable target speed
• wind entries on the DESCENT FORECAST page
• predicted use of anti-ice
The descent may be planned at economy Mach/CAS (based on Cost Index) or a
manually entered Mach/CAS. VNAV does not command an economy target speed
greater than VMO/MMO minus 16 knots or a pilot entered speed greater than
VMO/MMO minus 11 knots.
The FMC creates the descent path with a deceleration at the speed transition
altitude (typically 250 knots below 10,000 feet). VNAV plans a speed target 10
knots below the transition speed to allow for unknown tailwinds.
Descent path segments after the first altitude constraint waypoint are constructed
as straight line point-to-point segments. If the VNAV path segment is too shallow
to be flown satisfactorily at IDLE thrust, the FMC commands speed on thrust
levers (SPD). Elevators control the shallow descent path.
February 15, 2010
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