L-1011 Autoflight: Turbulence Mode (22-20)

Turbulence mode provides pilot-assisted, constant attitude flight through turbulent air. The autopilot control authority is reduced in order to soften its response to attitude changes caused by the turbulence.

Turbulence is an autopilot mode only and cannot be selected unless an autopilot is engaged. The TURB mode may be selected any time either autopilot is in CWS or CMD and A/L TRACK or GO AROUND is not established. The TURB light will illuminated indicating mode selection. Verification of mode engagement is accomplished by checking for TURB legend on in both AFCS MODES annunciators. When turbulence is selected while the autopilot engage lever is in the CMD position, the solenoid held lever drops from CMD to CWS. This action essentially cancels all other modes.

No other mode can be selected while the turbulence mode is engaged. The turbulence mode can only be released by pressing the TURB switch a second time or by disengaging the autopilot. Either of these actions then, is a prerequisite to resuming normal autopilot-controlled flight after a turbulence encounter.

If a flight director is also on when turbulence is selected, its command bars will be biased out of view but no FD warning flag will appear. When TURB is canceled, the command bars will return if the FD switch was left on but it will have a new reference. The new reference is the attitude existing at the time of TURB cancellation since all previous modes were canceled when TURB was selected.

L-1011 Autoflight: Control Wheel Steering Heading Hold (22-18)

If the bank angle is less than 3 degrees at the time CWS is engaged, the wings will roll level and the existing heading would be maintained.

L-1011 Autoflight: CWS Pitch and Bank Limits (22-17)

When an autopilot is engaged in CWS, the airplane will maintain the existing pitch attitude if it is less than 18 degrees and the existing bank angle if it is less than 35 degrees. If pitch or roll are more than 18 degrees respectively, the autopilot will return the airplane to these limits and then hold it there.

Therefore, pitch and bank limits can be manually exceeded through the control wheel. When control wheel pressure is released, the aircraft will automatically return to the maximum limits.

L-1011 Autoflight: Control Wheel Steering (22-16)

The two basic functions of control wheel steering are attitude hold and heading hold.

Control wheel steering allows the airplane to be hand flown with normal airplane feel. The airplane will remain where the pilot puts it as long as it is within the control wheel steering limits. That is, if you move the controls with a control pressure greater than four pounds, the airplane responds. When you release pressure on the controls, the airplane stays where you put it.

L-1011 Autoflight: Control Wheel Steering (22-9)

There are two basic modes of operation that an autopilot can be engaged in, control wheel steering (CWS) or command (CMD mode. In control wheel steering, the autopilot receives its pitch and roll inputs from the control wheel. The aircraft will remain where you put it. If you move the control wheel with a force of four pounds or more, the aircraft will respond. When you release the controls, the aircraft stays where you put it. Remember, only one autopilot can be engaged at a time.

When an engage lever is moved to CWS, it is held in that position electrically after the autopilot/flight director computer determines that the system is working properly. Anytime the signals are not valid, the lever will automatically drop to the OFF position.

Original Flight Hardware: Auto Pilot and Flight Director Engage Panel

The autopilot system of the Lockheed L-1011 was a very sophisticated system for its time. The avionic flight control system (AFCS) provides automatic modes of control throughout the total flight profile from takeoff run to landing roll. TheAFCS consists of 4 major subsystems:

1. Autopilot/Flight Director System (APFDS)
2. Stability Augmentation System (SAS)
3. Speed Control System (SCS)
4. Flight Control Electronic System (FCES)

The panel in today's posting, is the APFDS ENGAGE PANEL. It is located in the center of the glare-shield console.

The AUTOPILOT SWITCH has two solenoid-held switch positions besides the OFF position. Only one switch can be engaged at a time except when A/L (auto-land) mode is selected:

CWS

Engages A/P (only one can be engaged at a time) in the Control Wheel Steering mode to provide the following

• Pitch attitude hold up to +/- 18DEG
• Heading hold (if bank angle less than 3DEG)
• Roll attitude between 3DEG and 35DEG
• Auto pitch trim is operative except when force is being applied to control wheel/column.
• Control wheel electric trim is available
• Only Altitude Hold is available as an A/P command mode.

CMD

Has all the same functions as the CWS mode, but further has:

• Second AP can be engaged when A/L mode is selected
• any compatible NAV, HEADING/PITCH modes may be engaged
• auto pitch trim is operative

There are two flight director switches on the panel. One for the captain and one for the first officer. The modes of the flight director switch are:

• OFF - ADI command "V" bars biased out of view
• ON - Engages command bar display in the respective ADI. When the A/P is off, the V bars will simply display the roll attiude an the pitch attitude hold as set on the panels. With the A/P in CWD or CWS and no modes engaged, the V-bars display wings level or roll attitude and pitch attitude hold.
• SYNC - provides manual synchronziation of V-bars to heading or roll attitude when A/P is OFF.

The TURB (Turbulence) switch when pressed the first time reduces pitch and roll gains to 1/2, but does not change SAS. It disengages the auto-throttle system and all modes except GO-AROUND and A/L after A/L tracking has occurred. The switch also trips the autopilot to CWS if in CMD and removes the command bars from the ADI. The TURB mode is disengaged by pressing the switch again.




Panel Location