04/04/16
Overview
The autothrottle system supplies thrust control through the automatic adjustment of the throttle levers, during the full range of the flight.
The auto throttle system operates as a regulator of engine power from take-off to landing. It uses computers, servo actuators, and limiters to control the position of the throttle levers.
- The throttle quadrant operates as the primary actuator and limiter
- The integrated avionics computer (IAC) system has the processors and servo circuits that control the throttle quadrant
It also sends the mode of operation and indications of problems to the electronic flight-instrument system. The autothrottle agrees with the flight director and autopilot at all times.
The autothrottle has the functions that follow:
- Operation through the full range of available thrust for two engine operation
- Automatic operation from the start to the end of the flight
- Engine synchronized control
- Electronic Thrust Trim System (ETTS)
The autothrottle operates servomotors in the throttle quadrant through ARINC 429 busses. The pilot uses the flight-management (FMS)control-display-unit (CDU) to set the auto throttle in one of two modes:
- Speed control
- Thrust control
A navigation computer controls all of the auto throttle functions. The navigation computers are in the integrated avionics computers (IAC). There is a navigation computer in IAC 1 and IAC 2. IAC 3 does not contain a navigation computer.
The two navigation computers operate independently with only one in control at a time. Each throttle lever connects to a different autothrottle servo. The auto throttle that is on supplies the signals to the servo to set the throttle. It also supplies signals directly to the full-authority digital engine-controllers (FADEC) for small adjustments and synchronized inputs to the engines.
Integrated Avionics Computer (IAC)
IAC 1 and IAC 2 each house an autothrottle computer. They are resident on the FMS processor card and operate through that processor. The autothrottles operate in an active/standby configuration. There is an independent autothrottle servo for each throttle lever. There is no automatic transfer between autothrottle functions. The active autothrottle provides rate commands to the throttle quadrant assembly for throttle positioning.
The active autothrottle provides limited electronic engine trim commands directly to the FADEC for fine adjustment and engine sync and trim.
Throttle Quadrant
The throttle quadrant is installed on the center pedestal in the flight compartment. The throttle quadrant operates from 28 VDC.
The throttle quadrant serves as the primary flight deck controller for engine thrust control via two lever assemblies (one for each of the two engines).
Each throttle lever is capable of being driven by a servo integral to the throttle quadrant commanded by the A/T system via ARINC 429 databus. The throttle levers are usually manually operated by direct pilot input.
The TQA receives digital rate commands from the active autothrottle and moves the throttles accordingly. Throttle rate is fed back to the autothrottle digitally to close the loop.
The throttle quadrant provides throttle commands electronically to the EECs and FCUs via rotary variable differential transformers (RVDTs) coupled to the throttle levers.
The throttle quadrant has:
- Auto throttle switches (engage/disengage)
- Auto throttle quick-disconnect-switches
- Take-off/go-around switches
The autothrottle engage/disengage switches are on the pilot and copilot throttle levers. If the two engines are at the necessary engine pressure ratio (EPR), the switches engage the auto throttle and adjust the throttles to the correct position. The flight crew uses the switches to disconnect manually the auto throttle. This will also momentarily disarm the throttle quadrant servo motors.
The take-off/go-around (TOGA) switches are on the pilot and copilot throttle levers. If the pilot sets go-around, the auto throttle adjusts the throttles to a higher EPR supplied by the FADEC. If the pilot sets take-off, the auto throttle adjusts the throttles to the position necessary for take-off. The TOGA switches also engage the applicable flight director mode.
System Operation
Autothrottle Computer
The A/T provides closed loop speed and thrust control that is compatible with the flight director (FD) mode.
The FMS calculates the required EPR command from the aircraft inputs, and commands the throttle lever servo to drive the throttle to the required position. This places a power demand on the EEC which also computes an EPR command. This command is transmitted to IAC for comparison with the autothrottle EPR command, therefore providing closed loop control.
The EEC transmits the maximum EPR for the prevailing ambient condition, the idle EPR for engine limiter control and the actual EPR.
The A/T has two basic modes of operation:
- Thrust control for the following FD modes:
- T/O (takeoff)
- GA (go around)
- WS (wind shear)
- FLC (flight level change)
- Speed control
- For all other flight director modes
Note:
The default operation for the A/T is speed control when no FD modes are active. The A/T engage/disengage and quick disconnect functions are initiated via buttons on the throttle quadrant assembly.
An integrated function of the A/T is the electronic thrust trim system (ETTS), which provides limited authority thrust trimming. This is accomplished via ARINC 429 commands to the EEC, EPR trim, N1 synchronization, and N2 synchronization.
The A/T-ETTS software co-resides and co-executes with the FMS software in IAC 1 and IAC 2. Normal interfaces to the available I/O in the IAC are utilized.
Selection and mode control of the ETTS is done via the flight management system (FMS) control display unit (CDU) pages.
Electronic Engine Trim/Synchronization System
Trim System
The electronic engine trim system (EETS) is designed to command limited authority thrust changes via ARINC 429 commands transmitted to the EECs. The trim system performs TLA trimming to assist the A/T, as well as the pilot, at setting trimmed thrust when the system is selected to do so. In addition the trim system will perform N1/N2/ EPR synchronization when selected by the pilot.
The ETTS is a dual system and is integrated with the dual A/T system. Selection logic is located within the fault warning computers to select the single set of trim commands to be transmitted to the EECs.
The limited authority trim command consists of three components, added together to form a composite trim command, as follows:
- Sync command for N1 or N2 fan speed synchronization between engines
- TLA trim command for synchronization for EPR command between engines
- TLA position error trim command to account for throttle positioning inaccuracies when A/T is engaged (commanded vs. actual)
Synchronization System
The engine trim operating modes (N1 sync, N2 sync, EPR sync and OFF) are pilot selectable via an entry on a CDU page displayed by the priority FMS. The operating modes are mutually exclusive due to the selection scheme on the FMS menu, which allows only one mode to be active at a time. Selection of an operating mode arms the sync system for engagement, to provide sync control when the conditions and flight phase are appropriate to do so.
N1 synchronization is selected as the default setting when the FMS is powered up. Engagement logic to determine when each of the three trim command components are computed (non-zero) is based on the engine trim selected operating mode, A/T engagement status and phase of flight.
The phase of flight used for sync system mode operation shall be determined by the electronic trim system and consists of cruise (default), T/O, approach and G/A phases. These mutually exclusive flight phase are defined based on A/T mode and active autopilot/flight director pitch modes, listed in the following table:
Trim Phase of Flight
| TRIM PHASE OF FLIGHT | DESCRIPTION |
|---|---|
| Takeoff | Latched from time A/T T/O mode is enabled until A/T is disengaged, while T/O mode is no longer enabled or T/O (or Flex) thrust rating is off |
| Cruise | Active if no other phase is satisfied (includes level or non-level segments) |
| Approach | Active if aircraft configured for landing (flaps down and gear extended) or AP/FD Glideslope or Glidepath capture or Track mode is active |
| Go Around | Active if A/T G/A mode becomes active (based on Autopilot/Flight Director pitch mode) |
The engine synchronization system will compare engine speeds and for the selected shaft synchronization, compare a TLA trim value. The trim value (left-right) is transmitted to each channel of the EEC via ARINC 429. The trim value is added to the RVDT TRA value to generate the overall EEC EPR command in order to match the two engine speeds.
The following data is used by the Integrated Avionics Computer (IAC):
- N1 shaft speed
- N2 shaft speed
- EPR Command (EPR validated)
The EEC limits the trim authority to 5%. The trim authority is washed out at max power and idle setting.
Engine synchronization will operate with or without A/T engagement and can be selected by the pilot during takeoff but inhibited below 400 feet AGL.
Engine Electronic Controller
The engine electronic controller (EEC) provides the aircraft engine control functions and operates with the autothrottle. The electronic engine controller (EEC) is the interface between the autothrottle and the engine. The RVDT data from the throttle is transmitted directly to the EEC.
The EEC transmits the engine data to the autothrottle computer. This engine data is one of the parameters used by the autothrottle computer to determine throttle lever angle.
The autothrottle EETS function monitors the two EECs. The EETS function, when selected, provides any trim or sync adjustments to the EECs directly on ARINC 429 bus.
Autothrottle Selection
A/T 1/2 selection is accomplished through the MFD pop-up menu. With the autothrottle engaged, a change in autothrottle selection will cause the autothrottle to disengage.
Throttle Quadrant Assembly
The TQA houses the power levers and an independent autothrottle servo for each throttle lever. The control of engine thrust is achieved by modulation of the throttle lever. Movement of the lever is detected by a coupled dual-rotary variable differential transformer (RVDT) producing analog electrical signals dependent upon the lever position. The RVDTs are housed inside the TQA.
The TQA receives digital rate commands from the active autothrottle and moves the throttles accordingly. Throttle rate is fed back to the autothrottle digitally to close the loop.
The TQA also contains the A/T engage/disengage switches, the A/T quick disconnect buttons and the Go-Around (GA) buttons.
A/T Engage/Disengage Switches
- Interfaced to A/T 1 and AT/2
- Engage or disengage autothrottle
- Spring forces designed to prevent inadvertent operation
A/T Quick Disconnect Buttons
- Interfaced to A/T 1, A/T 2, FWC 1 (fault warning computer), and FWC 3
- Disengage autothrottle
- Direct disabling of servos
Go Around Buttons
- Interfaced to FGC via AFCS Guidance Panel
- Command go-around
- Accept windshear guidance
Each throttle lever is driven by a power drive integral to the TQA, which is commanded by the A/T via the ARINC 429 data bus. If necessary, the pilot can manually override the A/T by direct operation of the throttle levers.
Autothrottle Engagement/Disconnect
The autothrottle will always slave itself to the active flight director mode to provide complimentary control:
- Throttles operate in thrust mode for TO, GA, WS and FLC modes
- Throttles operate in speed mode for all other flight director modes
- Default operation for throttles is speed mode (no flight director mode active)
The autothrottle speed target bug is the speed reference bug displayed on the PFD airspeed scale. The speed reference may be set manually or from the FMS.
Autothrottle Engagement Inhibit
Autothrottle engagement is inhibited:
- On ground following touchdown (WOW and less than 50 knots)
- For invalid flight phases (phase of flight is determined by the FMS)
- Between 60 knots and 400 feet AGL during takeoff
- During the approach phase of flight when the retard mode would be active
Autothrottle Engagement
Autothrottle is engaged by toggling of the engage switches as follows:
- While on ground, with throttles less than 60% and airspeed less than 60 knots, arms the autothrottle for takeoff
- While on ground, with throttles greater than 60% while airspeed is less than 60 knots, engages the system directly into takeoff thrust control
- While in air above 400 ft, engages the system into a control mode, which is compatible with the active AP/FD mode. If no AP/ FD mode exists, the autothrottle engages into basic speed control mode
Autothrottle Disconnect
Autothrottle can be disengaged using the A/T engage/disengage switches or the quick disconnect buttons.
- Normal Disconnect (Manual or touchdown)
- A/T 1/2 annunciation on PFD turns red and is extinguished after two seconds
- Single aural Autothrottle announcement
- Abnormal Disconnect (inadvertent)
- A/T 1/2 turns red and flashes
- Continuous aural Autothrottle announcement until acknowledged
- Annunciation and aural canceled by pressing quick disconnect button
Throttle Positioning
The autothrottle computer receives inputs from aircraft systems. These are translated into a throttle position command, using the following values transmitted from the EEC.
- EPR max – maximum EPR for ambient conditions
- EPR idle – value of EPR at idle for ambient conditions
The autothrottle computer drives the throttle servo, thus moving the throttle to the desired position relative to the two values. The EEC reads the throttle position from the throttle RVDT angle (TRA).
The EEC outputs throttle lever angle (TLA) data in degrees, which is equivalent to the throttle RVDT angle (TRA) analog data received by the EEC.
TLA Measurement Angles
| THROTTLE LEVER SET POINT | TLA DEGREES ( 0.25 degrees) |
|---|---|
| Max Forward Range | 42.0 degrees |
| Full Mechanical Throttle Stop | 39.0 degrees |
| Max Forward Thrust (TOGA) | 37.0 degrees |
| Forward Idle (flat upper limit) | 2.0 degrees |
| Idle Stop |
TLA Trim
The EEC sends data to the autothrottle computer to calculate the required throttle lever angle (TLA) trim.
- EPR TLA: The EPR command value calculated from the current throttle position
- N1 shaft speed (for synchronization)
- N2 shaft speed (for synchronization)
- TRA Validated
When autothrottle is engaged, this data is used to adjust for any throttle positioning inaccuracies. The resultant TLA trim (in degrees) is transmitted to each channel of EEC on the ARINC 429 bus.
The EEC limits the trim authority to ±2 degrees TLA. The resultant trim value is added to the TLA value read from the throttle RVDT to generate the overall EEC EPR command. The trim is washed out at maximum power and idle power.
PFD Display Indications
Autothrottle engaged is displayed as a green A/T 1/2 to the left of the attitude sphere. The active autothrottle mode is displayed in green, to the left of the active lateral flight director mode on the PFD. The armed autothrottle mode is displayed below the active mode in white.
When limiting, LIM becomes the active mode. The amber LIM annunciation, which is used to indicate a speed or thrust limiting condition, will flash for about 10 seconds and then remain steady (not flashing) as long as the condition exists.
A normal A/T disconnect flashes the A/T 1/2 red and is timed out. An abnormal A/T disconnect flashes the A/T 1/2 red and is not timed out along with an autothrottle aural warning. This requires pilot acknowledgment by activating the A/T quick disconnect button.
PFD Annunciation Active Autothrottle Mode
| ACTIVE AT MODE | AT CONTROL MODE |
|---|---|
| TO (Green) | Takeoff Thrust Control |
| HOLD (Green) | Takeoff Throttle Hold |
| THRUST (Green) | Flight Level Change Thrust Control |
| SPD (Green) | Speed Or Mach Control |
| GA (Green) | Go-around Thrust Control |
| RETARD (Green) | Retard |
PFD Annunciation Armed Autothrottle Mode
| ARMED AT MODE | AT SUBMODES | AT CONTROL MODE |
|---|---|---|
| TO (White) | Armed to engage and provide Takeoff Thrust Control when throttles are advanced above 60% maximum thrust | |
| SPD (White) | LIM (Amber) | Structural limited (Gear, Flaps, Vmo, Mmo)or minimum speed limited or Power limited Speed/Mach Control |
| SPD (White) | LIM (Flashing Amber) | Indicates an airspeed deviation warning during power limited speed control. Airspeed is 30 knots above the speed target or 15 knots below the speed target. OR Airspeed is below the A/T speed lower limit (1.23 Vs) or above the A/T speed upper limit displayed on EFIS |
Autothrottle Takeoff Annunciation Example
| ACTIVE AT MODE | ENGAGE ANNUNCIATION | AT STATE |
|---|---|---|
| None | None | Aircraft on ground in a Takeoff regime but A/T is not armed for engagement. (Pilot has not pressed the A/T engage button to select the system or the system is failed) |
| TO (White) | A/T1 (Green) or A/T2 (Green) | Aircraft on ground in a Takeoff regime and is armed for T/O due to conditions being satisfied. A/T is armed for automatic engagement as a result of pressing of the A/T engage button |
| TO (Green | A/T1 (Green) or A/T2 (Green) | A/T is engaged in T/O Thrust control on ground following advancement of both throttle levers above 60% max. thrust while A/T is armed for engagement |
| Hold (Green) | A/T1 (Green) or A/T2 (Green) | A/T is engaged in T/O Throttle Hold between 60 knots and 400 ft AGL transition |
| T/O (Green) | A/T1 (Green) or A/T2 (Green) | A/T is engaged in T/O Thrust control above 400 ft AGL |
EICAS Display Indications
The A/T always limits the active engine rating for thrust. The active engine rating is selected automatically and displayed on the EICAS, based on phase of flight or manual selection by the crew.
Active Engine Rating
Primary flight phase calculation is performed by the FMS. The pilot may override the automatic rating selection through the thrust management pages in the FMS. EPR (engine pressure ratio) values are presented next to each available rating. Manual EPR set is available. Manual N1 set is available if the engine is in N1 control.
Engine Rating Bug
One rating bug is displayed on the EPR gauges at any time. The displayed rating bug is the active rating:
- Takeoff
- Max continuous thrust
- Max climb
- Max cruise
- Manual flex power
Power Reference Bug
The power reference bug on the EPR gauges represents the current EPR CMD. This is generated by the EEC and is displayed as a green T.
N1 Engine Control
Bugs are removed from the EPR gauges when N1 control is selected. The manual N1 set bug is displayed if set on the thrust management pages of the FMS. The commanded N1 comes from the EEC.
Engine Sync
Engine sync is available regardless of autothrottle engage state through the electronic engine trim system (ETTS). Engine sync modes are:
- N1 (default)
- N2
Selection of engine sync is accomplished through the thrust management pages of the FMS.
Sync Off
With the aircraft in cruise, either the A/T is engaged or disengaged, select sync to OFF. The absence of engine synchronization causes the SYNC annunciation to be absent from the EICAS main display.
N1 Sync Performance
With the aircraft in cruise phase of flight and sync select to N1, the right and left engines are being trimmed to the average of the two N1 commands. The LH and RH N1 values remain synchronized within the specified 0.08% limit, and the SYNC annunciation is displayed between the two N1 dials on the EICAS.
N2 Sync Performance
With the aircraft in cruise phase of flight and sync select to N2, the right and left engines are being trimmed to the average of the two N2 commands. The LH and RH N2 values remain synchronized within the specified 0.04% limit, and the SYNC annunciation is displayed between the system 1 and system 2 N2 indications on the EICAS.
Engine Trim
EPR Trim Performance
The engine trim performance function with EPR trim selected in the FMS, enables TLA trim commands to be sent by the A/T for all phases of flight. The TLA trim calculation will be dependent on the phase of flight and limited to 5% TLA. The SYNC annunciator is displayed between the two EPR dials on the EICAS.
Flight Phases and Modes of Operation
The A/T provides speed envelope limiting due to aircraft configuration such as Vmo/Mmo, flaps, slats, landing gear and low-speed protection, when in speed mode.
Takeoff
Takeoff Thrust Control Mode
The A/T is armed on the ground by pressing either engage switch. The armed T/O mode is displayed on the PFD in white.
The throttles automatically engage when the pilot moves the power levers past 23 TLA (this corresponds to 60% of available thrust).
Throttles then advance to takeoff power (TO EPR). At 60 knots the A/T is automatically placed in a hold mode until the aircraft is 400 feet AGL. Servo rate commands are zeroed by the A/T and servos are de-energized. After passing through 400 feet AGL, the A/T is slaved to the active vertical flight director mode.
Takeoff Throttle Hold Control Mode
The takeoff throttle hold control mode activates at 60 knots during takeoff roll to ensure that no undesirable thrust reductions are experienced during the critical phase of takeoff between 60 knots and 400 ft AGL.
- The servo rate commands are zeroed by the autothrottle
- The servo drives (clutch command) are disabled by an independent monitor in the FWC function
Controlling the rate commands from the autothrottle and the clutch commands from the FWC provides redundancy. If for some reason oneof the commands is not taken away, the other command ensures the autothrottle will still go into takeoff hold during this critical phase of flight.
After passing through 400 feet AGL, the autothrottle is slaved to the active vertical flight director mode.
Flight Level Change Thrust Control Mode
Climb and Descent
The flight level change thrust control mode is activated upon pilot selection of the FD flight level change mode (FLC) or when the FMS engages in VFLC.
A/T provides climb or idle power based on the altitude selection which instructs the pitch axis to climb or descend. Large flight level change climbs cause the A/T to advance the throttles to the upper EPR rating. Large flight level change descents cause the A/T to retard the throttles to the active lower EPR rating.
For small flight level change climbs and descents, the A/T uses a proportionality scheme which provides thrust as needed to attain a programmed rate of climb and descent. A target vertical speed is set based on the altitude change. The A/T sets power to achieve that speed within operating limits.
- The programmed rate of climb/descent control is proportional to the magnitude of the selected altitude change
- Small flight level change climb/descent control is provided to ensure passenger comfort
Note:
There is no speed protection in thrust mode.
Airspeed Control Mode
The A/T provides a complementary mode to the active vertical flight director mode for cruise (typically speed control).
The airspeed control mode is the basic mode of the A/T. The airspeed control mode accommodates both airspeed and Mach control.
The speed/mach targets are obtained from the selected PFD during manual control and from the FMS during FMS speed control.
IAS vs. Mach mode is controlled automatically, or by the pilot during manual speed target control. IAS vs. Mach mode is controlled automatically by FMS during FMS speed control.
The airspeed control mode provides high- and lowspeed envelope protection.
- Vmo/Mmo, placard speeds, and green line (1.23 Vs)
The A/T annunciates the structural speed limited condition and/or the power limited control condition via a LIM indication on the PFD. The airspeed control mode provides full flight regime EPR rating protection.
Speed Bug Management
Active Speed Bug
The A/T is slaved to the active speed bug which is controlled on the guidance panel and displayed inside the airspeed tape. Active speed bug is cyan if manually controlled and magenta if FMS controlled.
Inactive Speed Bug
Inactive speed bug is displayed as a reference outside of the airspeed display. It appears as an unfilled arrowhead and represents the bug that is not selected as active.
The inactive speed bug provides additional pilot selectable reference if the active bug is controlled by FMS. It also provides indication of FMS speed command if the selected bug is manual.
Approach
The autothrottle provides a complementary mode to the active vertical flight director mode for approach (typically speed control). Dual sensoraveraging is used during dual couple approach.
Retard Mode
The retard mode provides a fixed rate retard of both throttle levers to the idle stop during aircraft landing flare. The retard mode is available for both AP/FD coupled and non-coupled approaches. The retard mode activates based on a radio altitude of < 50 feet while the aircraft is in a landing configuration (gear down and landing flaps). Upon touch down, the A/T fully disconnects automatically.
Go-Around and Wind Shear
Upon selection of either of these flight director modes, the throttles advance to the maximum thrust position. The A/T go-around mode provides a fixed rate throttle advance to the maximum takeoff EPR rating. The go-around mode is also activated if the throttle is engaged and the pilot presses the GA button to accept windshear guidance.
Emergency Descent Mode
The airspeed target continuously synchronizes to Vmo/Mmo minus 10 knots.
If Mach is the selected airspeed type in the red IAS/Mach digital readout on the PFD, the display automatically transitions from Mach to IAS when the aircraft descends through 32,400 feet (9,875 meters).
The manual speed bug is placed at a position corresponding to the airspeed target and is also shown in red.
While the EDM is active, the speed target is not selectable manually with the SPD knob on the guidance panel. The FMS/MAN position change of the SPD knob has no effect and the FMS speed bug is indicated by a magenta triangular symbol on the outside of the airspeed tape.
The speed target is set at 250 knots when ASEL becomes the active FD mode during transition to level flight.
System Interface
Signal Interface
Autothrottle System Interface
IAC 1 and IAC 2 each house an autothrottle computer. Each autothrottle computer can send analog servo rate commands to control the TQA servo and receives the servo rate command feedback from the TQA via ARINC 429.
FWCs monitor the WOW and speed status to send servo clutch commands from A/T to engage the TQA servo when the logic meets the required conditions.
TQA A/T quick disconnect/disengagement signal is sent to A/T in IACs to disconnect the A/T.
Engine sync commands from the A/T ETTS system are sent through the FWCs to EECs via ARINC 429.
A/T data from EECs are sent to DAUs via ARINC 429.
Power Inputs
The power inputs to the autothrottle system are as follows:
- IAC 1 is powered from SPDA 2 DC battery bus
- IAC 2 is powered by SPDA 4 DC essential bus
- IAC 3 is powered by SPDA 1 DC battery bus
- TQA is power by 115 VAC bus 1
- TQA servo is powered by SPDA 1 DC bus 1
System Monitoring
Autothrottle Annunciations
Autothrottle engage/disengage annunciations are displayed above the attitude sphere and to the left of the attitude source annunciation. Autothrottlemode annunciation is displayed to the left of the lateral flight director mode annunciations at the top of the PFD. Autothrottle engagement is annunciated by a green A/T 1/2.
Normal autothrottle disengage is annunciated by a red A/T 1/2. Abnormal autothrottle disengagement is annunciated by a continuous flashing red A/T 1/2. This requires pilot acknowledgment by pressing the autothrottle quick-disconnect button. The active autothrottle mode is displayed in green to the left of the lateral flight director mode. Armed autothrottle modes are displayed in white. LIM is in amber.
System Test
Operational Test
There are three autothrottle tests which can be initiated through LRU TEST page on CAIMS.
They are:
- IAC autothrottle test
- Autothrottle switch test
- A/T TQA wraparound test
IAC Autothrottle Test
This test verifies all inputs into the autothrottle system. These inputs include each LRU received on the ASCB by the selected A/T.
Autothrottle Switches Test
This test verifies the correct disconnect and engage/disengage switch functions for each A/T. The switches tests which are defined for this installation of autothrottle are:
- A/T quick disconnect switch
- A/T engage switch
A/T TQA Wraparound Test
When this test is selected, the A/T/ETTS will move the throttles forward and back to ensure closed loop functionality with the TQA.
