C. Liftoff -------- After liftoff (unsquat), the F/D transfers from a 15 degrees nose up command to a speed command. The initial speed target is V2 plus 20 knots, however, the MASI (mach airspeed indicator)cursor is at V2. The transition to speed control is a function of altitude rate beginning at 600 fpm (feet per minute) and completed at 1200 fpm. Maximum speed command is limited to the flap placard speed until the MCP speed is reached. The F/D bank angle is limited to 8 degrees and roll rate to 4 degrees/second below a radio altitude of 400 feet. At radio altitude greater than 400 feet, the master light associated with the F/D ON is extinguished. The bank angle limit is increased to the MCP selected bank angle. At UNSQUAT PLUS 17.5 seconds and a radio altitude greater than 400 feet, the A/T changes to and annunciates ARM. Other DFCS and A/T mode may be selected. However, ALTITUDE ACQUIRE is inhibited prior to a radio altitude of 800 feet.
D. Climb -------- pressing the VNAV and LNAV switch engages the FMC for vertical and lateral guidance. LNAV and VNAV are annunciated. Pressing the VNAV switch also initiates the N1 mode. The N1 mode switch illuminates, and N1 is annunciated for A/T and CLB is annunciated for thrust. When the radio altitude is greater than 400 feet, the A/P may be engaged in CMD. The master light associated with the A/P in CMD is illuminated. When the A/P is engaged, the speed trim system is disengaged and auto stabilizer trim is engaged.
Fig. 39-2 LNAV
[3] Figure 39-2 illustrates LNAV operation sequence. LNAV is the normal lateral navigation cruise mode for the DFCS. The lateral flight profile commands are supplied from the FMCS based on the navigation and performance data bases and the active flight plan. The FMCS inhibits LNAV engage when airplane on the ground.
A. Initial condition -------- after TAKEOFF, the radio altitude is greater than 400 feet.
B. LNAV (Lateral navigation)----- Press LNAV switch to engage LNAV. The LNAV command originate within the FMC and are processed in the FCC. The normal flight path starts on the runway, therefore , the airplane is on the active flight plan path. Figure 39-2 shows a normal capture, the airplane flies to the active leg at an intercept angle of less than 90 degrees. The message "NOT ON INTERCEPT HEADING " appears on the FMC CDU scratch pad to alert the pilot to correct the heading when the airplane is not on a correct intercept. If LNAV is engaged while on an intercept heading, the A/P commands are based on that heading to capture the active leg.
C. Arrival preparation --------- approach preparations for the LNAV mode should be completed before reaching the last waypoint in the flight plan. Apaaroach preparations consist of selecting or entering the approach procedures on the FMCS CDU and pressing EXEC (execute key) . FMC commands cause the airplane to arrive at the optimum localizer capture point with the correct intercept angle.
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本文链接地址：第31课 大气数据系统 LESSON 31 AIR DATA SYSTEM(41)
