1)  Before the takeoff mode can be entered, either or both flight directors must be on and all A/P CMD ENGAGE switches must be off. The F/D only configuration is verified by the AFDS status FMA on the EADI. The IAS/MACH indicator is set at V2 (climb speed); HDG is set to the heading of the initial flight leg after takeoff; and ALT is set for the initial clearance altitude.

 (b)  
Flight Director Display

 1)  Initially (A) the EADI shows wings level and rotation attitude of 8 degrees nose up. The status FMA shows F/D and both the pitch and roll operative mode FMAs show TO.
 2)  On reaching 5 feet altitude (B), roll channel commands provide track hold and the pitch rotation attitude command reduces linearly toward zero within 3 seconds. The roll operative mode FMA changes to TRK HLD.
 3)  The F/D enters the takeoff speed engage mode (C) which produces pitch attitude commands to maintain a safe climbout speed.
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A
757
MAINTENANCE MANUAL

MODE CONTROL PANEL FIRST
CAPTAIN'S FLIGHT OFFICER'SDIRECTOR SWITCH (EXAMPLE)
FLIGHT DIRECTOR SWITCH
A/P MAY BE ENGAGED IN CMD

EADI DISPLAY EADI DISPLAY EADI DISPLAY

A

Takeoff Mode (F/D Only)
Figure 9

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D00392
A

757
MAINTENANCE MANUAL

 (c)  Mode Transitions
 1)  From the takeoff mode, transition into the following modes is possible: roll channel, HDG HLD, HDG SEL, LNAV ARM, and LNAV capture; pitch channel, ALT HLD, V/S, FLCH, and VNAV. The takeoff mode ends when the A/P is engaged, when both F/Ds are switched off, or when transition to the above modes are accomplished.
 (5)  
Autopilot/Flight Director System Roll and Yaw Modes Logic (Fig. 10)

 (a)  
Takeoff Mode Logic

 (b)  
When either Flight Director is switched ON, F/D engage logic enables the takeoff mode. The on-ground condition generates roll attitude washout logic which produces a roll F/D command of wings-level. At five feet radio altitude, the Track Hold mode is automatically engaged. This changes the roll F/D commands from wings-level to track hold.

 (6)  
Autopilot/Flight Director system Roll and Yaw Control Signals Flow (Fig. 11)

 (a)  
Takeoff Mode Control Signal Flow

 (b)  
When the F/D is turned ON and the airplane is on the ground, the F/D command processor integrator is set to wings-level. The difference between roll attitude and the integrator output is roll attitude error. The roll error is combined with body roll rate and pitch attitude to produce the roll F/D bar command which is applied to the EADI. The wings-level command is provided until the in-air condition is sensed.

 (c)  
The in-air condition occurs when the radio altitude is five feet or greater. At this time, adjusted track is used as the input to the heading hold synchronizer and the turn direction command processor. However, heading hold logic disables the integrator in the heading hold synchronizer so that only adjusted track is used to produce the F/D heading command. The F/D heading command is applied to the roll F/D command processor when the roll attitude washout logic goes to zero at five feet radio altitude. The input is limited by the position of the bank angle (B/A) limit switch on the MCP.

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