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must be set up in the FMC in order to use VNAV. If the specific approach is
available in the FMC and a gradient path exists, modification of the approach is
not necessary and compliance with stepdown fix altitude restrictions inside the
FAF, if indicated, is guaranteed.
If the specific approach is not available in the FMC then an overlay may be
selected, such as the ILS approach when the glideslope is inoperative. In this
event, the FAF altitude may have to be modified to comply with the approach
plate. In addition, stepdown fix altitude restrictions inside the FAF, if indicated,
will have to be evaluated to determine gradient path compliance.
Stepdown fix compliance may be evaluated in the following manner:
· Insert the named stepdown fix waypoint into the LEGS page at the
appropriate point and leave the airspeed / altitude line blank.
· Close up the discontinuity.
· Line select the airspeed / altitude line for the entered waypoint.
· Evaluate the altitude readout in the scratchpad.
737 Sec. 3 Page 221
Flight Manual Continental Rev. 11/15/02 #41
· After evaluation reselect the appropriate approach from DEP/ARR and
restore the FAF altitude modification, if necessary. Do not reenter the
stepdown waypoint.
If the gradient path is determined to comply with the stepdown, plan to use
VNAV. If the gradient path does not comply with (at-or-above) the stepdown,
plan to use V/S and ensure stepdown altitude compliance.
Manual Waypoint Entry
When there is no procedure available in the FMC data base, manual entry of a
series of waypoints may be accomplished to define the approach routing. The
waypoints may be defined by using names of waypoints or navaids in the data
base. Raw data monitoring and course compliance is required. Verify the
accuracy of the FMC approach creation.
VREF SELECTION
VREF is selected on the APPROACH REF page for the desired final flaps. The
FMC generates a Target speed by adding the VREF selection to the WIND
CORR line value (default of +5 knots). If reported surface winds require an
additive greater than 5 knots, adjust the WIND CORR line accordingly. Check
that Target speed generates on the LEGS page as the speed for the last approach
waypoint (RWxx or MAxx).
USE OF VNAV
VNAV should not be engaged until on course in LNAV or on course in
VORLOC with a compatible FMC course selected. The FMA must be
monitored to ensure the intended mode.
The point of VNAV engagement during or in transition to the approach is
dependent upon circumstances. It is not uncommon for ATC to impose a speed
restriction that would be incompatible with VNAV control of the airspeed. Use
of V/S or LVL CHG may be more appropriate and convenient until approaching
the FAF. Coordination with ATC may be necessary to allow configuration and
deceleration to Target speed prior to the FAF. Selecting VNAV between the
typical configuration points of 4nm and 2nm is easily managed when earlier
engagement is not feasible or convenient.
Sec. 3 Page 222 737
Rev. 11/15/02 #41 Continental Flight Manual
Using VNAV for descent on the gradient path from the FAF to minimums
requires the setting of zero (“0”) in the MCP altitude window. If continuing the
use of VNAV from a course transition and through the final segment zero can
be set when clearance for the approach is received and with VNAV PTH
maintained on the FMA. If VNAV is not utilized in transition or for stepdowns
outside the FAF set zero when obtaining ALT HLD at the FAF altitude and
engage VNAV during the configuration process approaching the FAF. When
approaching the FAF, if VNAV will not engage or cannot be maintained, ensure
zero is set and plan for the use of V/S to initiate descent from the FAF.
Note: When VNAV is engaged, monitor the FMA for VNAV PTH annunciation
and ensure compliance with approach altitudes.
With VNAV engaged the MCP speed window will be blank and VNAV will
control the speed for flap selections. During configuration with VNAV engaged
the “SPEED” and “TARGET” calls will be made at the appropriate time and
the airspeed monitored to ensure compliance.
USE OF VERTICAL SPEED (V/S)
Vertical Speed is used as a primary mode when a gradient path does not exist or
when VNAV is inoperative. Vertical Speed may also be used as a backup
mode for VNAV. Planning and briefing the use of V/S as a backup may
preclude the need for a go-around if difficulties with VNAV are experienced.
In many cases, the approach chart itself will provide convenient vertical speed
reference for the specified gradient path. The appropriate rate is chosen based
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737 FLIGHT MANUAL 737飞行手册2(46)
