Thrust Reduction
Climb thrust is selected by pushing the N1 switch or, on airplanes equipped with automatic thrust reduction, automatically upon reaching the thrust reduction altitude.
VNAV Engagement
VNAV commands an airspeed increase to the planned climb speed profile, limited by configuration.
VNAV Climb
The VNAV climb profile uses VNAV SPD at the default climb speed or pilot selected climb speed to remain within all airspeed and altitude restrictions that are part of the SID entered into the active route. Autothrottle uses selected climb thrust limit.
Note: Selection of ENG OUT on the CLB page provides the crew with advisory
engine out performance information. (Prior to U7.5) If activated all
subsequent performance predictions are blanked and VNAV is unavailable
until a climb page other than ENG OUT is activated.
If the climb speed profile cannot achieve an altitude constraint, the UNABLE NEXT ALTITUDE scratchpad message is shown.
Climb Restrictions
VNAV enters the VNAV PTH mode to remain within departure or waypoint restrictions. Speed maintained during this time can be:
.
procedure based speed restriction
.
waypoint speed restriction
.
default VNAV climb speed
.
manually entered climb speed.
Top Of Climb (T/C)
The point where the climb phase meets the cruise altitude is called the top of climb. Approaching this point, the FMC changes from the climb phase to the cruise phase. The T/C is displayed any time the FMC computes a transition from a climb phase to a cruise phase, such as a step climb.
The T/C point is displayed on the map as a green open circle with the label T/C.
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11.31.18 June 8, 2001
Flight Management, Navigation -Flight Management System Operation
737 Operations Manual
Cruise
At cruise altitude, the FMC sets cruise speed at the default or pilot entered speed until reaching the top–of–descent (T/D) point. Alternate cruise speed options are:
.
long range (LRC)
.
flight crew entered speed. Cruise thrust is set as required to maintain level flight at the target speed, with the
autothrottle engaged. The FMC uses maximum range cruise speed if cost index is set to zero. Fuel and ETA predictions are based on a constant altitude cruise unless a step
climb altitude is entered.
Step Climb
If a step climb altitude is entered in the CRZ page STEP altitude, the FMC
calculates the point where the step climb should begin.
The distance and ETA to the next step point are shown on the CRZ and
PROGRESS pages.
The next step point is shown on the map as a green open circle with the label S/C.
Descent
VNAV can perform a descent in either of two modes – path descent or speed descent. During a path descent, the FMC uses idle thrust and pitch control to maintain a vertical path, similar to a glideslope in three dimensions. During a speed descent, the FMC uses idle thrust and pitch control to maintain a target descent speed, similar to a level change descent.
Top Of Descent (T/D)
The point where the cruise phase changes to the descent phase is the top of descent. T/D is calculated from an end of descent (E/D) point.
The T/D point is displayed on the map as a green open circle with the label T/D. On airplanes with FMC update U7.2 and on, intermediate T/D points show on the map as green open circles with the label T/D-XXXXX (altitude). Intermediate T/D points exist when path segments between altitude constrained waypoints produce a level path segment. The intermediate T/D point shows where the descent will resume.
Flight Management, Navigation -Flight Management System Operation 737 Operations Manual
End of Descent (E/D)
The FMC calculates a descent path based on airspeed restrictions, altitude restrictions and the end of descent (E/D) point. The E/D point is shown on the map as a green open circle with the label E/D. The E/D is the last of the following which is not preceded by a lateral discontinuity:
.
(U7 and on) the runway threshold for approaches with a runway waypoint
on the RTE LEGS page, or
.
(U7 and on) the missed approach point for approaches not showing a
runway waypoint on the RTE LEGS page, or
.
the lowest “at” altitude restriction if no arrival procedure is entered.
Entering an instrument arrival procedure provides an E/D point.
If there is no E/D point, FMC predictions assume a computed profile to 1000 feet above the destination field elevation, at a position which will vary according to selection of arrival procedures. The FMC will provide a slowdown profile for approach. VNAV path descent is not available if there is no E/D point.
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