第31课 大气数据系统 LESSON 31 AIR DATA SYSTEM(44)

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D. Preparation for climb two ------ when ATC clearance is given to a cruise altitude, the MCP altitude is set equal to the FMCS cruire altitude. The A/P ALT HOLD and SPEED mode switches illuminate and ALT HOLD and V/S (vertical speed) ARM for AFDS and MCP SPD for A/T are annunciated. The A/S cursor now driven to MCP speed.
E. Climb two -------- climb is initiated by pressing the VNAV mode switch on the MCP. The VNAV mode switch and N1 mode switch illuminate and all others are off. The A/P now commands speed error from the FMC, the A/T is controlling thrust to a climb N1 from the FMC.
F. Level off at FMCS cruise altitude -------- The A/P acquires and holds the FMCS cruise altitude . The A/T follows FMCS guidance to transition from climb N1 to cruise speed. When a new cruise altitude is desired, it is selected on the MCP and on the FMCS CDU cruise page. Climb is initiated by pressing EXEC key on the FMCS CDU.
G. Climb Three ------ The A/P changes to VNAV SPD guidance and the A/T changes to climb N1 guidance. The airplane climb to the new altitude under FMCS guidance.

[2] Figure 40-2 illustrates an example of the descent phase.

 

 

 

 

 

 

                  Fig. 40-2   VNAV  descent

VNAV descent path are projected by FMC during cruise operation. The FMC continually computes the top of descent and the end of descent based on active flight plan and navigation and performace data bases. VNAV descent is almost automatic and its goal is to get the airplane to the glideslope capture point by the most economical means. LNAV must remain valid to make a VNAV path descent.
A. Initial condition -------- with the A/P in CMD, VNAV engaged and the MCP altitude set equal to the FMC cruise altitude, the A/P and A/T are commanded to the FMC described vertical path. Prior to reaching the top of descent( T/D), a lower altitude must be selected on the MCP.
B. Descent one ------ At T/D, the FMC provides guidance to the A/P and A/T to command the VNAV descent path. In VNAV descent path, if 255 knots is exceeded below 10,000 feet, FMC sets LVL CHG (Level change) reversion request.
C. Level off at BARON altitude ------- FMC direct A/P to command a level off at the BARON (the last waypoint) altitude.
D. Descent Two ------ Preparation for a descent consists of selection of a lower altitude on the MCP. At top of descend ( T/D) , the FMC provides guidance to the A/P and A/T to command the VNAV descent path.
E. Level off at MCP altitude -------- Acquiring the MCP ALT causes the A/P to command a level off at the MCP altitude even though this deviates from the VNAV descent path.
F. Descent three -------- Selecting a new MCP ALT causes the VNAV switch light to go out and the ALT HOLD and SPEED mode switches to illuminate. A/T command and airspeed target are changed to MCP speed. VNAV path descent is initiated by pressing the VNAV mode switch on the MCP. FMC provides vertical speed guidance to the A/P and A/T to recapture the VNAV path.
　
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