Engine Inoperative Climb
The engine inoperative climb speed is approximately maximum angle climb speed and varies with gross weight and altitude. At high altitudes and weights, a fixed Mach is used as an upper limit on the engine out climb speed. Engine out climb speed is the FMC default used during climb when ENG OUT CLIMB is selected. Select ENG OUT CLIMB after flap retraction and all obstructions are cleared.
If a thrust loss occurs at other than takeoff thrust, set maximum continuous thrust on the operative engine and lower the nose slowly to maintain airspeed as the thrust loss occurs.
Note: Selecting CON on the TMSP or the FMC THRUST LIM page (as
installed) moves the N1/EPR bug to maximum continuous thrust until
another mode is selected or automatically engaged. Thrust must be
manually set.
In the clean configuration, select the engine out prompt on the CDU climb page. The engine out mode provides VNAV commands to climb at engine out climb speed to cruise altitude, or maximum engine out altitude, whichever is lower. If the airplane is currently above maximum engine out altitude, driftdown information is available. Upon reaching level off altitude, the command speed changes to engine out LRC. Leave thrust set at maximum continuous thrust until airspeed increases to the commanded value.
Note: If computed climb speeds are not available, use flaps up maneuvering speed and maximum continuous thrust.
Cruise
This section furnishes general guidance for the cruise portion of the flight for maximum passenger comfort and economy.
Maximum Altitude
Maximum altitude is the highest altitude at which the airplane can be operated. It is determined by three basic characteristics, which are unique to each airplane model. The FMC predicted maximum altitude is the lowest of:
.
maximum certified altitude - determined during certification and is
usually set by the pressure load limits on the fuselage. The maximum
certified altitude may not be exceeded.
.
thrust limited altitude - the altitude at which sufficient thrust is available
to provide a specific rate of climb. (Reference the Long Range Cruise
Maximum Operating Altitude table in the PI chapter of the QRH).
Depending on the thrust rating of the engines, the thrust limited altitude
may be above or below the maneuver limited altitude capability.
.
maneuver limited altitude - the altitude at which a specific maneuver
margin exists prior to buffet onset (minimum 0.2g for FAA or 0.3g for
CAA/JAA operation). These margins provide 33° (FAA) or 40°
(CAA/JAA) of bank angle protection to buffet.
Although each of these limits are checked by the FMC, thrust limitations may limit the ability to accomplish anything other than relatively minor maneuvering. When at or near the FMC maximum altitude, it is possible for LNAV inputs to exceed the capability of the airplane. This could result in loss of altitude or airspeed. This risk may be reduced by changing the FMC parameters (maintenance action) to suit individual operator needs.
Fuel predictions may be inaccurate at or above the maximum altitude and are not displayed on the CDU. VNAV is not available above FMC maximum altitude. Fuel burn at or above maximum altitude increases. Flight above this altitude is not recommended.
The maneuver speed indication on the speed tape (as installed) does not guarantee the ability to fly at that speed. Decelerating the airplane to the amber band may create a situation where it is impossible to maintain speed and/or altitude because as speed decreases airplane drag may exceed available thrust, especially while turning.
Optimum Altitude
Optimum altitude is the cruise altitude for minimum cost when operating in the ECON mode, and for minimum fuel burn when in the LRC or pilot-selected speed modes. In ECON mode, optimum altitude increases as either airplane weight or cost index decreases. In LRC or selected speed modes, optimum altitude increases as either airplane weight or speed decreases. On each flight, optimum altitude continues to increase as weight decreases during the flight.
For shorter trips, optimum altitude as defined above may not be achievable since the TOD (top of descent) point occurs prior to completing the climb to optimum altitude.
Flight plans not constrained by short trip distance are typically based on conducting the cruise portion of the flight within plus or minus 2000 feet of optimum altitude. Since the optimum altitude increases as fuel is consumed during the flight, it is necessary to climb to a higher cruise altitude every few hours to achieve the flight plan fuel burn. This technique, referred to as Step Climb Cruise, is typically accomplished by initially climbing 2000 feet above optimum altitude and then cruising at that flight level until 2000 feet below optimum. For most flights, one or more step climbs may be required before reaching TOD. It may be especially advantageous to request an initial cruise altitude above optimum if altitude changes are difficult to obtain on specific routes. This minimizes the possibility of being held at a low altitude/high fuel consumption condition for long periods of time. The requested/accepted initial cruise altitude should be compared to the thrust limited or the maneuver margin limited altitudes. Remember, a cruise thrust limited altitude is dependent upon the cruise level temperature. If the cruise level temperature increases above the chart value for gross weight, maximum cruise thrust will not maintain desired cruise speed.
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本文链接地址：757 Flight Crew Training Manual 机组训练手册(36)
