CONCORDE SST

Automatic Fight Control Systems

Concorde has an Automatic Flight Control System (AFCS) installed, that for the 1970s was state of the art. The system is designed to allow "hands off" control of the aircraft from climb out to landing. There are 2 mains parts to the system; the Autothrottles and Autopilot, and a number of associated systems, such as the warning displays and test systems.

The majority of the controls for the AFCS are situated on the glareshield and are shown below in the picture. This is from Air France Concorde F-BTSD, but the British Airways Concordes have the exact same system. Roll the mouse of the picture to define the various control areas (coming soon).

AUTOPILOT

The central area is the area we are most concerned with, as this is where we actually set up the Automatic Flight Control regimes.

AUTOPILOT

The top row of the panel can be split into 3 sections to select different autothrottle and horizontal or vertical autopilot modes. The lower row allows the headings to be set into the system, as well as height and speed "to fly to" settings. It also includes six "piano switches" that can select in or out in the autothrottles, autopilot and flight director systems as required.

The flight director provides a visual indication on the pilot's Attitude Direction Indicator (ADI - Artificial Horizon) what the autopilot would want to do if it were flying the aircraft under the current settings. The Flight Director (FD) is used when the pilot wants to hand fly the aircraft, but be guided by the autopilot. It displays 2 yellow command bars and an attitude display on the ADI, that the pilot would match with the aircraft's movements.


AUTOTHROTTLES

The Autothrottle system provides electronic thrust control of the engines, to ensure certain speeds can be held during cruise and approach flying. Each engine can be switched to 3 control modes: Main, Alternate and OFF! A facility is also provided to disconnect the autothrottle for one engine at a time during abnormal operations.

As the throttles are not mechanically, but electrically connected, a main and standby channel are both engaged, with the main channel being given priority.

If the Autothrottle system detects a fault it will automatically disengage and hold a constant throttle settings. The autothrottles can also be "primed" to come into operation when a certain parameter is meet, eg the aircraft is required to level out at a certain height

The primary control of the autothrottle system's settings are through the controls available on the left quarter of the glareshield panel and a datum adjust unit on the centre pedestal.

AUTOTHROTTLES
There are 3 main Autothrottle modes:

MACH HOLD - This will ensure the engines are automatically throttled to maintain the current mach number being followed when this mode was engaged. This is using during cruise, as it will maintain the correct mach number no matter what the outside conditions are that effect mach number, such as temperature.

IAS HOLD - This the the mode that the throttles will selected to first, and will hold the Indicated Air Speed (IAS) that the aircraft was flying at when they were engaged

IAS ACQ - The 3rd mode will allow the aircraft to fly or aquire to a set air speed. Eg on approach the aircraft could be flying at 250 knots, with the next speed being 210 knots. This can be dialled in and then, when requested to 210 knots by ATC, the model selected. When 210 knots is achieved, the mode will revert to IAS HOLD.

The dual systems are selected on by the piano switches, only one is used, with the other acts as a back up. Disconnects are also available on the outside of the main throttle leavers.

On the datum adjust unit, on the centre pedestal, The speed can be tweaked if required.

AUTOPILOT

Concorde is fitted with 2 Autopilot systems. Only one is engaged at a time to operate the aircraft and the 2nd is available as a hot spare. Both system are engaged if the aircraft is carrying out an AutoLand, with the 2nd system automatically available should the primary one fail. The autopilot has 5 horizontal and 12 vertical modes of operations. Also on the panel is the commonly used altitude to fly to setting, which is used for the majority of the flying, after the initial take off.

The Autoland system on Concorde is very sophisticated and can land the aircraft better than the pilot on many occasions! It uses the Airport Instrument landing System's (ILS) Glideslope and Localiser to guide the aircraft to the touchdown point. Just before landing, data form the radio altimeters is feed into the AFCS to flare and land the aircraft. The pilot, does however, have to stop the aircraft.

Similar to the Autothrottles, there are 2 piano switches that engage the Autopilot. These are solenoid latched and will only latch if all the supporting systems are functioning correctly; such as the Air Data Computers, Autostabilisation systems, navigation and compasses. The system will always engage in the heading and pitch hold modes, and can be easily disconnected from a thumb switch on the Yoke.

AUTOPILOT HORIZONTAL MODES
HORIZONTAL MODES
INS - This mode causes the aircraft to track between two waypoints that are being fed to it from the external Inertial Navigation System (INS)

TRK HDG - Track or Heading. The selector dial on the bottom row is either pulled for Heading mode or pushed for Track mode, and the aircraft will follows the Track or Heading selected on the dial. A heading will follow a compass direction, where as a Track will follow a direct route to the selected position taking into account wind speeds etc..

HDG HOLD - This is the basic autopilot mode and will cause the aircraft to follow the heading it was flying when it was engaged.

VOR LOC - When this is pressed it causes the aircraft to turn and track the selected VOR beacon or localiser that has been selected. The is a Prime mode and a small triangle under the button will light up when the capturing is in progress. Once the beacon or localiser has been acquired the button will light.

BACK BEAM - Technically this is not a Autopilot mode, but a Flight Director mode and will only operate when the Autopilot is disengaged. It permits tracking of a Back Beam localiser

AUTOPILOT VERTICAL MODES
AUTOTHROTTLES

PITCH HOLD - This is the basic mode of the autopilot and will hold the existing aircraft pitch when engaged. It comes on as default when the Autopilot is engaged.

MACH HOLD - This function will hold the current Mach number by pitch changes and not throttles changes. If the autothrottles are engaged they will take precedence and the autopilot will default to PITCH HOLD

MAX CLIMB - This is selected at or near Vmo (Maximum operating speed) and will hold the airspeed to a figure around Vmo. As the speeds approached Vmo at the top of the climb it will disengage and hold the speed with pitch changes.

MAX CRUISE - This engages shortly after Mach2 and is an extension of MAX CLIMB. It is normally used in conjunction with the autothrottles primed in MACH HOLD to keep he aircraft flying at Mach2.0.
If the aircraft begins to overspeed, due to temperature changes, the auto throttles will slow the aircraft down. Once back at the correct speed MACH HOLD will disengage and MAX CRUSE will re-engage. It also prevents the aircraft exceeding the maximum operating temperature (Tmo) of 127 degrees Celsius on the tip of the nose.

IAS HOLD - Holds the current indicated airspeeds by means of pitch changes

ALT HOLD - Holds the aircraft existing altitude.

VERT SPEED - Sets up the aircraft to hold a vertical speed as set up on the vertical rate of climb indicator

ALT ACQ - Similar to IAS ACQ on the autothrottles. A preset altitude to fly to can be programmed in on the selector, and when the ALT ACQ Button pressed the aircraft will fly to that altitude. the prime light will light during the operation and the button will itself light when the speed is acquired.

TURB - Turbulence mode, only used in moderate or severe turbulence. It holds the existing pitch attitude and heading, it reduces the trim rate of the electric trim system to smoothen the ride.

LAND - Automatic landing mode. When this is pressed the prime triangle will light. It causes the aircraft to capture the glideslope AND and track to localiser that has been selected. When the glideslope has been captured the button will light and the small triangle prime light under the button will go out. The VOR/LOC button will light when the localiser has been captured. During the capture process the prime light on VOR LOC will light. After LAND mode is selected the 2nd autopilot can be engaged for redundancy.

GO AROUND - Indicates an automatic go around has been initiated. This is carreid out when more than 2 of the throttle leavers are moved fully forward in LAND or GLIDE Modes. It will pitch the aircraft up at 15 degrees and hold the wings level until the next command is made by the crew.

GLIDE - This is used when expected that the pilot will not carry out an automatic landing and simply wants the aircraft to automatically fly the path down to the runway, where he will take over for a manual landing

When this is pressed it caused the aircraft to capture the glideslope AND and track the selected VOR beacon or localiser that has been selected. The Prime light (triangle)will lit when engaded and the will go out, when the when the glideslope has been captured and button will light. The VOR/LOC mode is also selected when this is pressed. Its prime triangle will light up once the beacon or localiser has been acquired.

 

ADDITIONAL AFCS COMPONENTS

 
The additional features of Attitude Direction Indicator (ADI) are a key part of the system:

It feedsback information from the flight directors, and warnings to the pilot of a failure in parts of the AFCS.

As this is one of the pilot's primary flying instruments, he can see instantly what the fault is. eg a Flight director malfunction or a warning that the radio altimeter data is suspect etc....

A switch is available to select from which flight director, information is fed into the ADI.

Datum Adjust Unit

Depending on the mode, a small adjustment to the settings on the AFCS configuration can be made manually.

The parameters that can be adjusted are:

  • Autothrottle speed setting (+/- 22knots or +/- 0.06 Mach)
  • Autopilot turn - this will turn the aircraft at a roll rate of 5 degrees per Second. This in HDG/TRK mode will cause a revision in the basic heading mode.
  • Pitch datum adjust - Various settings depending on Mode, eg ALT HOLD, or MACH HOLD
Warning and Landing Display

  • AP / AT - Red lights will light / flash if the Autopilot of Autothrottle system is no longer functioning correctly
  • DH - Decision height warning will light when under the set height
  • LAND 2 and LAND 3 light - These will be green if the AFCS is working, and available to support an automatic landing in CAT2 or CAT3 conditions
  • Aircraft Deviation Lights - white bars either side of the amber aircraft will light to show the aircraft is veering off the glide slope or localiser. It would be expected that the AFCS would automatically correct for this deviation and these would go out.
  • A test button tests all the lamps in this panel

Diagrams and specific infomation based on "Flying Concorde" by Brian Calvert and the Concorde Flying Manual.