Low Altitude Level Off
Occasionally a low altitude climb restriction is required after takeoff. This altitude restriction should be put in the MCP altitude window. When the airplane approaches this altitude prior to selection of a pitch mode, the pitch mode annunciation changes from TO to ALT CAP.
When the pitch flight mode annunciation changes from TO to ALT CAP, the autothrottle engages into the EPR/N1 mode to maintain the takeoff power setting. For proper speed control, either manually retard the thrust levers or set the desired target airspeed into the MCP IAS/Mach window and select the autothrottle SPD mode.
Note: For airplanes with manual climb thrust selection, the CLB switch must be
selected prior to selecting the autothrottle SPD mode to preclude
exceeding climb thrust limits.
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.
Climb Speed Determination
Enroute climb speed is automatically computed by the FMC and displayed on the climb and progress pages. 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. Reference speeds are also provided for maximum angle climb (MAX ANGLE) operation.
The ECON climb speed is a constant speed/constant Mach schedule optimized to obtain the minimum airplane operating cost. The constant Mach value is set equal to the economy cruise Mach calculated for the cruise altitude entered in the FMC.
For very low cruise altitudes the economy climb speed is increased above normal values to match the economy cruise speed at the entered cruise altitude. For ECON climb, the speed is a function of gross weight (predicted weight at top of climb), predicted top of climb wind, predicted top of climb temperature deviation from ISA, and cost index.
Engine Icing During Climb
Engine icing may form when not expected and may occur when there is no evidence of icing on the windshield or other parts of the airplane. Once ice starts to form, accumulation can build very rapidly. Although one bank of clouds may not cause icing, another bank, which is similar, may cause icing.
Note: The engine anti-icing system should be turned on whenever icing
conditions exist or are anticipated. Failure to follow the recommended
anti-ice procedures can result in engine stall, overtemperature or engine
damage.
Economy Climb
The normal economy climb speed schedule of the FMC minimizes trip cost. It varies with gross weight and is influenced by cost index. The FMC generates a fixed speed schedule as a function of cost index and weight.
Economy climb speed normally exceeds 250 knots for all gross weights. FMC climb speed is limited to 250 knots or flaps up maneuvering speed, whichever is greater, below 10,000 feet (FAA Airspace). If ATC permits the use of a higher speed below 10,000 feet, the use of ECON speed may provide additional fuel savings.
Economy Climb Schedule - FMC Data Unavailable
.
250 knots/VREF 30 + 80, whichever is higher- Below 10,000 feet
.
290 knots/.78 Mach - Above 10,000 feet
Maximum Rate Climb
A maximum rate climb provides both high climb rates and minimum time to cruise altitude. Maximum rate climb can be approximated by using the following:
. flaps up Maneuver Speed + 50 knots until intercepting Mach 0.76
Note: The FMC does not provide maximum rate climb speeds. Maximum Angle Climb
The FMC provides maximum angle climb speeds. Maximum angle climb speed is normally used for obstacle clearance, minimum crossing altitude or to reach a specified altitude in a minimum distance. It varies with gross weight and provides approximately the same climb gradient as flaps up maneuvering speed.
