Avionics Bending: APFDS Engage Panel - Part 1

L-1011 APFDS Engage Panel

The next component of the Lockheed L-1011 Autoflight system is the APFDS Engage panel. This panel is located in the middle of the L-1011 Glare Shield (see below)

The panel has switches for the Autopilot A and B as well as the Left and Right Flight Director (FD). The Autopilot of the L-1011 as both a Control Wheel Steering (CSW) modes as well as a full Command (CMD) mode. Both the A and the B system of the auto flight systems work independent unless the aircraft is in Approach/Land (A/L) mode during which both automatic flight systems are required. 

The panel that I am using for this demo and the test integration with X-Plane is one of several APFDS Engage panels we have at the museum. This particular panel is a little beaten up, but, it makes for a great test instrument. The switches on the panel have long extensions and are frequently called "bat-switches". The flight director switches are normal toggle switches with the SYNC position having a spring return. The autopilot swathes are magnetic latch switches that will be held in certain positions by solenoids. For example, if the the autopilot system is not ready, the switches can not be moved out of the OFF position, or, if engaged and the pilot presses the A/P Disengage switch on the control wheel ... the bat switches will return to the OFF position. Below is a short video showing the action of the switches as well as a schematic of the panel taken from the WDM fiche.

APFDS Engage Schematic - From L-1011 WDM

L-1011 Autoflight: Command Modes (22-10)

Once an autopilot lever has been placed in CMD or or command, it continues to act as if it were in control wheel steering until pitch or roll command modes are engaged.

Command modes are selected by pressing the switchlights along the top of the autopilot panels. Only one pitch mode and one roll mode can be selected at a time. Selection of a second pitch or roll mode will automatically disengage the first pitch or roll mode. Selection of a command mode will cause both autopilot computers to operate in that mode even though only one computer is engaged.

The switchlight for each mode will illuminate to show positive mode selection.

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.

L-1011 Autoflight: Flight Director Command Bars (22-8)

As you already know, each flight director switch connects its respective autopilot/flight director computer to command bars on the same side. Autopilot A to the Captain's command bars, autopilot B to the First Officer's command bars. Either or both flight directors may be selected simultaneously and are independent of autopilot engagement. With the flight director switch off, the command bars are biased out of view as shown on the First Officer's side. Placing the flight director switch to ON will bring the command bars into view as shown on the Captain's side.

In the pictured example:

Autopilot/flight director computer A will now provide steering information to the Captain since both autopilot autopilot levers are off, but the FD for the Captain's side is on. With Autopilot lever A on, autopilot A would fly the aircraft in pitch and roll and the flight director command bars would indicate to the Captain what the autopilot is doing.

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