Vertical Angles (U7 and on)
A vertical angle can be assigned to a waypoint from the navigation database. This vertical angle defines a VNAV path between the waypoint and the waypoint preceeding it. This feature can be available in approaches, approach transitions, and STARs. For example, the vertical angle for the glidepath of an ILS approach, would typically be 3 degrees. This angle is displayed on the ACT RTE LEGS page above the speed/altitude line for the associated waypoint. Vertical angles may be expected in any approach ending at RWXXX or MAXXX. The E/D will be RWXXX or MAXXX, and the E/D altitude will be either threshold crossing height (TCH – typically 50 feet above the touchdown zone elevation) or the altitude specified at MAXXX.
Flight Management, Navigation -Flight Management System Operation 737 Operations Manual
If a VNAV PATH 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.
If the vertical angle leg becomes active during a SPEED descent, the VNAV mode will change to VNAV PATH automatically, and there will be no SPEED prompt on the descent page.
Early Descent
A descent in VNAV started before the top of descent point is an early descent. If a path descent is planned, VNAV commands a 1000 fpm descent until the idle descent path is intercepted. If a speed descent is planned, VNAV commands an idle thrust descent.
To start an early descent, (prior to U10) use CAPTURE or (U10) use DES NOW prompt on the DES page.
CAPTURE/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.
CAPTURE/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.
VNAV Use During Approaches (U7 and on)
VNAV will remain engaged at all flap settings, allowing approaches to be flown using the vertical angle guidance. Speed for final approach can be set on the APPROACH REF page.
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737 Operations Manual
If an ILS approach is flown in VNAV using the vertical angle guidance, VNAV will disconnect when passing the GS–XXX point, but it can be reengaged. If the GS–XXX point is deleted, VNAV would remain engaged throughout the approach.
For an approach without a runway waypoint on the RTE LEGS page, the VNAV path is calculated to the MDA or a calculated altitude at the missed approach point. The calculated altitude may be below the MDA to make sure a flight path angle and normal threshold crossing height.
Note: It is the flight crew’s responsibility not to descend below the MDA until adequate visual contact is achieved.
Go–Around (U7 and on)
Below 2000 feet radio altitude, go-around is engaged when a TO/GA switch is pushed. The thrust limit is set to go-around. If VNAV is subsequently engaged, the thrust limit changes to climb and VNAV commands pitch to follow the missed approach procedure.
Upon initiation if TO/GA, a new cruise altitude will be automatically assigned and will appear on the FMC pages. The new cruise altitude will be the highest of:
.
the highest restriction in the missed approach routing
.
default value of 1500 feet above airport elevation, or
.
MCP altitude.
However, if the MCP altitude is the lowest of the three, the airplane, with autopilot engaged, will level off at the MCP selected altitude.
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Flight Management, Navigation -Flight Management System Operation 737 Operations Manual
VNAV Cruise (Engine Out Above Eng Out Max Alt)
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Engine Out Modification
Select the ENG OUT prompt on the CRZ page. The ENG OUT page displays the appropriate engine out driftdown performance data to enable the airplane to descend to the engine out maximum altitude. Refer to FMC Cruise, section 11.42 for a complete description of the ENG OUT CRZ page.
Drift Down Execution
After selecting the ENG OUT CRZ page and (U5 and on) the left or right ENG OUT mode, perform the driftdown as follows:
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