757 AMM 飞机维护手册 自动飞行 AUTOFLIGHT 1(169)

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 2)  Roll attitude and roll attitude command are summed to produce roll attitude error. This error signal is summed with body roll rate, differentiated and summed with aileron servo position feedback to produce wheel rate. This is then applied to the aileron trim integrator which sets max and min values for surface deflection. After integration, wheel rate becomes the aileron servo command which is applied to the electrohydraulic servo valve (transfer valve). The amplitude of the aileron servo command determines the rate of response (roll rate) while the duration of the command determines the bank angle achieved.
 (e)  As the airplane turns toward the selected heading, the difference between magnetic and selected heading is reduced. Both the aileron servo command and the roll F/D command are reduced in magnitude. When the heading is within capture limits, the roll attitude washout logic is generated and the airplane rolls to wings level. The heading hold made is then engaged.
 (14) Attitude Hold Mode (Fig. 13)
 (a)  
The roll mode engaged after CMD ENGAGE depends on airplane attitude, airplane dynamics, and the Lateral Command Engage Option (LCEO). The baseline configuration is LCEO inoperative.

 (b)  
GUN 001-050, 052-999; with LCEO inoperative, the airplane rolls to wings level and engages in heading hold mode regardless of the bank angle at the time of engagement.

 (c)  
GUN 051;
 With LCEO operative, three variations exist:

 

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MAINTENANCE MANUAL

 

RESPONSE FOR BOTH FLT DIRECTORS OFF, OR EITHER FD ON IN T/O OR G/A MODE
IF FD ON AT CMDENG, AP ENGAGES INTO CURRENT FD MODE (SEE AP MODE ENGAGE OPTION)

NORMALLY HDGMAG = HDGTRU IF HDGTRU SELECTED

GUN 051

Attitude Hold Mode Figure 13
D00434
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 1)  If the bank angle is less than 5 degres, the airplane rolls to wings level and engages in heading hold mode.
 2)  If the bank angle is between 5 and 30 degrees, the airplane engages in roll attitude hold.
 3)  If the bank angle is greater than 30 degrees, the airplane is rolled to a 30-degree bank angle and engaged in the attitude hold mode.
 (d)  AIRPLANES WITH CONTROL WHEEL STEERING; attitude hold is the basic CWS submode (Fig. 11A). It is automatically selected when the wheel force after CWS ENGAGE is less than | 2 lbs, the roll rate is less than 0.5 deg/sec, and the airplane is in a bank angle of 5 degrees or more.
 (15) Lateral Navigation (LNAV) Mode (Fig. 14)
 (a)  
In the LNAV mode, the FMC provides lateral steering commands to the FCC to follow a selected flight plan. Applicable controls on the MCP for this mode are the LNAV switch/light and the HDG display.

 (b)  
LNAV ARM Mode (A)

 1)  The LNAV ARM mode is initiated during HDG SEL (roll engaged mode) by pressing the LNAV switch/light. The mode is annunciated on the EADI. The AFDS commands to hold selected heading until a valid LNAV steering command is received from the FMC at LNAV capture.

 (c)  
LNAV Capture (B) and Capture Turn (C)

 1)  At LNAV capture, the FMC supplies valid lateral steering command (LNAVC). Detection of LNAVC changes the roll active mode to LNAV and the EADI roll engaged annunciations change to LNAV and LNAV ARM. The LNAVC commands a right turn to acquire flight plan track at WPT 1.

 (d)  
LNAV Mode (D)

 1)  The FMC supplies LNAVC to maintain the FMC flight plan track from WPT 1 to WPT 2. Automatic compensation is applied to compensate for wind drift. There is no change in EADI indications. The FMC provides lateral steering commands at WPT 2 for a left turn to acquire the outboard track.
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