Lateral PCA Control
Track Mode—In the lateral axis, controlled differential thrust provides precise track angle control and dutch roll damping (.g. 11(a)). The pilot uses the autopilot TRK knob command (selectable in integer degrees) to select the desired track. Track is preselected by turning the knob to the desired track, then commanded by pulling the knob. This command is compared with the sensed track angle, generating a track error. This error is converted into a bank
Commanded

Left bank angle
engine roll thrust Commanded Commanded command bank angle track angle
Pilot
Bank input

+
–

Command – Track limit knob
HDG/TRK
toggle

Right Sensed button engine track angle bank roll thrust
angle command
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Gain  S 1  Integrator limit logic 

Left
engine
pitch thrust
command

Right
engine
pitch thrust
command

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angle command and compared with the sensed bank angle, generating a bank angle error, with the maximum bank angle command limited. Normal MD-11 bank angle limits can be selected on the outer part of the Heading/Track (HDG/TRK) knob, up to a limit of ± 20° . An integrator with a low gain is provided to trim out biases in the lateral axis. For stabilization and dutch roll damping, bank angle, yaw rate, and roll rate feedback are available. The resulting differential thrust commands are issued to the wing engines to obtain the commanded track. The pilot’s track command is displayed by a bug on the compass and a vertical bar on the PFD (.g. 12), as well as on the navigation display cursor (.g. 2(c)).
Bank Angle Mode—The bank angle mode was an alternative to the track mode. If the crew selected HDG rather than TRK, only for this PCA implementation, the bank angle mode was activated. The HDG/TRK knob became hot (meaning it responded as turned without having to be pulled) and could command bank angles of up to ± 20° . When in the bank angle mode, the track command and track feedbacks, shown in .gure 11(a) were zeroed. Figure 13 shows the bank angle mode readout on the FCP and on the PFD roll window, which was the commanded bank angle—000° to 020° for right banks and 340° to 000° for left banks. While obviously not a suitable annunciation for a production application, this served well for a .ight test.
Flight control panel

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Primary flight display
Flight control panel

Primary flight display 970595

Longitudinal PCA Control
Longitudinal control is designed to provide precise .ightpath control and adequate phugoid damping. In the pitch axis, the simplest control law operates only the two wing engines on the MD-11 (.g. 11(b)). The pilot input through the autopilot thumbwheel command for .ightpath angle is limited, then compared with the sensed .ightpath angle, and limited again; PCA .ightpath commands were limited from +10° to –10° , and errors to ± 3° . A low-gain integral path is provided in pitch to eliminate steady-state errors, and pitch rate feedback is provided to assist in phugoid damping. Collective (equal) thrust commands are sent to the wing engines to obtain the commanded .ightpath. The thumbwheel .ightpath command selected on the FCP is displayed to the pilot on the PFD using the existing .ightpath command bar (.g. 12). In the V/S mode (.g. 13), the commanded vertical speed was shown on the FCP in the V/S window and with a bug on the vertical-speed scale on the right side of the PFD.
Figure 14 shows the control laws that include the center engine. Two modes were available. In one mode (.g. 14(a)), the center engine provided trim speed control. In the second mode (.g. 14(b)), the center engine also had a short-term, pitching moment control; the center engine received opposite-sign thrust commands for pitch control, washed out with a 4-sec time constant.
　
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