.
CLB 2 is approximately a 20% derate of climb thrust. Reduced thrust climb may also be automatically selected by the FMC depending

upon the amount of thrust reduction made for takeoff by either the fixed derate or assumed temperature method. Climb thrust reductions are gradually removed as the airplane climbs until full
climb thrust is restored. If rate of climb should drop below approximately 500 feet per minute, the next higher climb rating should be selected.
Prior to takeoff, the pilot may override the automatically selected climb thrust limit after the takeoff selection has been completed by selecting another climb thrust limit on the N1 LIMIT page. When the automatically selected climb thrust limit is overridden, the previously selected takeoff derate is not affected.
Note:  Use of reduced thrust for climb increases total trip fuel and should be evaluated by each operator.

Climb Constraints
Climb constraints may be automatically entered in the route when selecting a procedure, or manually entered through CDU entry. When the airplane levels off at an MCP altitude, that altitude is treated as a climb constraint by the FMC.
All hard altitude climb restrictions, including “at or below” constraints, should be set in the MCP altitude window. The next altitude may be set when the restriction has been satisfied or further clearance has been received. This procedure provides altitude alerting and ensures compliance with altitude clearance limits.

When relieved of constraints by ATC, use of LVL CHG or VNAV with MCP altitude intervention (as installed) is recommended in congested areas, or during times of high workload. Altitude intervention (as installed) is accomplished by selecting the next desired altitude in the MCP altitude window, pushing the MCP ALT INTV switch which deletes the altitude constraint and allows the airplane to climb to the MCP altitude.

Low Altitude Level Off
Occasionally a low altitude climb restriction is required after takeoff. This altitude restriction should be set in the MCP altitude window. When the airplane approaches this altitude, the mode annunciation changes to VNAV ALT (as installed) and the airplane levels off. For airplanes without VNAV ALT installed, the mode annunciation initially changes to ALT ACQ, then ALT HOLD.
Note:  If ALT ACQ occurs before N1 is selected, automatic thrust reduction occurs and the autothrottle speed mode engages.
High Takeoff Thrust - Low Gross Weight
When accomplishing a low altitude level off following a takeoff using high takeoff thrust and at a low gross weight, the crew should consider the following factors:
.  
altitude capture can occur just after liftoff due to the proximity of the level
off altitude and the high climb rate of the airplane

.  
the AFDS control laws limit F/D and autopilot pitch commands for
passenger comfort

.  
there may not be enough altitude below the intended level off altitude to
complete the normal capture profile and an overshoot may occur unless
crew action is taken.

To prevent an altitude and/or airspeed overshoot, the crew should consider doing one or more of the following:
.  
use reduced thrust for takeoff at low weights whenever possible

.  
reduce from takeoff to climb thrust earlier than normal

.  
disconnect the AFDS and complete the level off manually if there is a
possibility of an overshoot

.  
use manual thrust control as needed to manage speed and prevent flap
overspeeds.

Transition to Climb
Maintain flaps up maneuvering speed until clear of obstacles or above minimum crossing altitudes. If there are no altitude or airspeed restrictions, accelerate to the desired climb speed schedule. The sooner the airplane can be accelerated to the climb speed schedule, the more time and fuel efficient the flight.
Copyright . The Boeing Company. See title page for details.
FCT 737 (TM) October 31, 2006

Climb Speed Determination
Enroute climb speed is automatically computed by the FMC and displayed on the climb page. It is also displayed as command speed when VNAV is engaged. Below the speed transition altitude the FMC targets the transition speed limit stored in the navigation data base for the departure airport (250 knots below 10,000 feet MSL in FAA. airspace), or flaps up maneuvering speed, whichever is higher. The FMC applies waypoint-related speed restrictions displayed on the LEGS pages, and altitude-related speed restrictions displayed on the climb page.
The FMC provides optimum climb speed modes for economy (ECON) operation and engine out (ENG OUT) operation. These optimum speeds can be changed before or during the climb. Selectable climb speed modes are also provided for maximum angle climb (MAX ANGLE) and maximum rate (MAX RATE) operation.
　
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