11.05.2 Autoflight Flashcards
What are the autoflight subsystems? (5)
- Autopilot (AP),
- Flight Director (FD)
- Auto throttle System (ATS)
- Automatic pitch trim system (auto trim),
- Yaw Damper System (YD).
What is the primary task of autoflight?
reduces the pilot’s workload by controlling the flight automatically
What does flight director do?
shows the pilot how to fly the aircraft manually using the
command bars in the Primary Flight Display (PFD) or Attitude Director Indicator (ADI).
What does yaw damper do?
- improves the dynamic stability of the aircraft during the whole flight
- controls the rudder to dampen Dutch roll oscillations during the entire flight.
What does autotrim do?
maintains pitch stability during all phases of the flight, usually by automatically adjusting the horizontal stabilizer
What are the three aircraft axes?
- the longitudinal, X-axis
- the vertical, Z-axis
- and the lateral, Y-axis
What flying control surfaces are used to control pitch?
Horizontal stab (pitch trim) and elevator
What flying control surfaces are used to control roll?
Ailerons and flight spoilers
What flying control surfaces are used to control yaw?
Rudder
What are aircraft with electronic AP systems called?
EFCS systems
What are the two loops of autoflight called?
- inner loop
- outer loop
What two channels are used in the inner loop for autoflight?
- pitch channel
- roll channel
What does the autoflight inner loop control?
Aircraft attitude
How does the autoflight inner loop control aircraft attitude?
- the comparison between the actual attitude of the aircraft and the commanded attitude.
- The result of the comparison is called the ‘attitude error signal’
- this basically drives the flight control surfaces
Where are autopilot inner loop actual attitude signals from?
from the aircraft’s attitude sensors (vertical gyro or the
IRU)
Where are autopilot inner loop commanded attitude signals from?
comes from selections made by the pilot or from the
outer loop
What does the autopilot outer loop control?
The outer loop controls the aircraft to automatically capture and stabilize a flight path
How does the autoflight outer loop control aircraft flight path?
- comparison between a commanded value (the desired path) and the actual flight path.
- The result of the comparison is called the ‘path error signal’
- this is converted by the autopilot to the attitude command signal for the inner loop
What angle is roll attitude limited to in autoflight?
30 degrees
What angle is pitch angle limited to in autoflight?
25 degrees nose up and 10 degrees nose down
How many autopilots are used during cruise?
Only one at a time during normal flight
What are the three AP engage selections?
- OFF - The autopilot is not connected to the flight controls.
- CMD - Command position engages the autopilot for automatic flight, using the calculated signals from the inner and outer loops.
- CWS - The Control Wheel Steering position (middle) activates the CWS function and only the inner loop of the autopilot is active to control the aircraft attitude. The pilot uses the control wheel or column to change the attitude
What is the difference between the CMD and CWS selections?
- CMD uses both inner and outer loops
- CWS just uses inner loop
How is autopilot disengaged?
The autopilot can be disengaged on the control panel by pressing the ‘disengage bar’ or by moving the autopilot lever to off.
Normally the autopilot is disengaged by pressing the red quick disengage pushbutton located on each control wheel.
What are checked for autopilot interlocks?
- Electrical power – Power to the autopilot.
• Disengage Switch - No disengage switch is pressed.
• Manual Trim - No manual trim switch is activated at the control wheel.
• Pitch/Roll – Valid pitch and roll attitude signals (important)
What are the autopilot disengage warnings?
The disengage warning consists of a red flashing warning light or corresponding message on the Primary Flight Display (PFD) and most aircraft have an aural warning.
When are autopilot disengage warning also triggered?
The warning is always triggered when the engage lever drops to the “off” position, independent of the reason
How are autopilot disengage warning reset?
- reset signal from the quick disengage pushbuttons on the control wheel/side stick
- pressing the autopilot “off“ warning light if available
- The warning can also be cancelled when the autopilot is re-engaged.
What is used to engage autopilot system to control surface?
- Smaller or older aircraft use an electrical autopilot servomotor which is directly connected to the cable system near the control column
- A second way of autopilot integration into flight controls is to use an autopilot hydraulic motor integrated inside the Hydraulic Power Unit
- The final integration used in large commercial aircraft is a separate hydraulic motor that is only used for the autopilot
When does the autopilot clutch close?
When all autopilot interlock conditions are fulfilled,
How does the pilot take back manual control?
By disengaging the autopilot
What is used in case an AP disengage is not possible due to system fault?
Override device
How much force does the pilot have to generate in CWS for transducers to generate a voltage?
20N
What are the three autopilot safety levels?
- Fail safe
- Fail operational
- Fail passive
How many autopilot systems are required for fail safe?
one
How many autopilot systems are required for fail passive?
two
How many autopilot systems are required for fail operational?
three
In fail operational, what happens if one system fails?
Continues to operate as a fail passive system
How can fail passive operation be obtained with only one AP system?
- Instead of having 2 independent autopilots a second channel to the single autopilot is added.
- The monitor channel is fully separated and by performing comparisons, can detect a wrong signal, fulfilling the “fail passive” function.
Where are the flight director (FD) indications always located?
- The Flight Director (FD) indication is always in the same indicator as the Artificial Horizon.
- This is either in the Attitude Director Indicator (ADI) or Primary Flight Display (PFD)
What do the two FD command bars represent?
Roll commands - called the roll bar (vertical line) and
Pitch commands - called the pitch bar (horizontal line)
What are the FD command bars displayed WRT?
This information is displayed with reference to the aircraft symbol
What is another method of displaying attitude information on FD instead of command bars?
- by using the V-bar.
- The V-bar is a single command bar giving both pitch and roll information at same time,
Where are the FD command bars when the AC is on the correct flight path?
- The Flight Director command bars will be centred whenever the aircraft maintains the desired attitude or flight path
- or when the pilot follows the directions given by the Flight Director Computer (FDC).
When else are the FD command bars located in the centre?
The ‘bars’ are usually centred when the autopilot is active controlling the flight and is used by the pilots to monitor the autopilot performance.
When are the command bars visible?
- FD power is switched on,
- FD computer is valid,
- FD must be switched on by the operator,
- All necessary FD signals are valid.
When is the FD flag in view?
- When the Flight Director Computer has no electrical power available and/or the computer has a fault.
- The flag in the ADI also appears when there is an indicator failure, for example when the roll bar is blocked mechanically.
In heading hold mode, what happens if the roll signal is less than 5 degrees?
the autopilot rolls the aircraft to wings level and keeps the actual heading
If a mode is selected in FD and AP is engaged, what happens?
the autopilot will automatically activate this mode
What are the three AP/FD mode groups?
- Roll modes
- Pitch modes
- Common modes
What are the two AP mode categories?
- Basic modes - Become active when the autopilot is engaged to Control Wheel Steering (CWS) or command.
- Upper modes - Must be selected by the pilot, usually from the control panel. This is only possible when the autopilot is engaged to command.
Where is the TO/GA switch located?
On the throttles
What happens if TOGA is selected on the ground?
the ‘take-off’ mode is activated on the Flight Director
How are active and armed modes indicated on flight mode annunciator panel?
- Active modes - are shown in green and
• Armed modes - are in amber colours
Where else are active and armed modes indicated?
Another technique uses small prisms which can change the position to show different modes
What are the modes in the first line of PFD display?
1st line always shows the engaged or active mode in green colour
What is shown in the 5th column on PFD?
AP/FD engagement status
What are the different flight phases?
- Take-off.
• Thrust reduction altitude - Altitude where the engine thrust is reduced.
• Climb phase.
• Cruise phase - For most of the flight,
• Descent phase.
• Approach - To destination airport.
• Landing or Go-Around - if the aircraft cannot land.
How high, above the runway, does landing phase start?
50ft above the runway
What does yaw damper reduce?
Dutch roll oscillation
Which way is the rudder deflection in yaw damp?
deflect the rudder in the direction which opposes the direction of the yaw motion.
What other circuit does the yaw damp system need for accurate rudder movement?
Speed adaption circuit
What is used to distinguish between dutch roll and a steady turn?
- Band-pass Filter - This circuit allows the computer to differentiate between a Dutch roll oscillation and a steady turn
- The yaw rate signal only passes the band-pass filter when it changes in level with the typical Dutch roll frequency of the aircraft (usually about 0.25Hz).
How does the pilot deflect the rudder?
Rudder pedals
What relevance do the yaw damper signals have to the pilot?
Preflight reassurance that the system is working correctly
How is manual pitch trim applied?
Manual trimming of the stabilizer is done by the pilot using the trim switch on the control wheel
The rudder deflection is always the ___ of the yaw damper input and the pilot input and is called a ‘______ yaw damper’
The rudder deflection is always the SUM of the yaw damper input and the pilot input and is called a ‘SERIES yaw damper’
When is pitch trim automatically carried out?
When AP is engaged
What does Mach trim prevent?
Tuck under due to increasing mach number
What does alpha trim prevent?
prevents high angle of attack during high speed flights
Why must elevator deflection not be maintained to trim aircraft?
because of the high air pressure applied to the elevator
What happens when the first trim system fails?
- usually a second system takes over automatically.
- If the remaining system also fails then the pilots must be
alerted to take corrective action
What indications are there when elevator deflection exceeds threshold for 10 seconds?
- A caution indication like this Autopilot ‘OUT OF TRIM’ light comes on
- or CAS message
What are two types of autothrottle system?
- classic auto throttle system which uses a servomotor to adjust the throttle position and the mechanical linkage to the engines.
- The second system is used in modern fly by wire Airbus aircraft. It delivers a digital signal directly to the FADEC computer of the engine.
What does the autothrottle thrust mode control?
Controls either the Engine Pressure Ratio (EPR) or the N1 rotational speed to the desired value.
What does the autothrottle speed mode control?
Controls the calibrated airspeed of the aircraft’s desired value comes from the Flight Management system (FMS) or selected by the pilot
Which autothrottle speed mode is used for takeoff?
Thrust mode
What signals are disconnected when takeoff thrust is reached (autothrottle)?
the auto throttle switches off any command to the throttles
Which autothrottle modes are used for the following:
- Climb
- Cruise
- Descent
- Climb - speed or thrust modes
- Cruise - speed mode
- Descent - speed or thrust modes
What autothrottle mode is used for go-around?
thrust mode
What does autothrottle do during flare manoeuvre?
retards the throttles slowly to the ‘idle’ position.
What does the autothrottle clutch between the servo and the throttles ensure?
enables the auto throttle system to drive the throttles without preventing manual inputs from the pilot
What do the throttle protection circuits prevent?
To prevent an engine overboost
What inputs does the thrust rating computer need for accurate calculations?
- Total Air Temperature (TAT) from the ADC and
• Altitude from the ADC.
What inputs does the thrust rating computer need for accurate calculations?
- Total Air Temperature (TAT) from the ADC and
• Altitude from the ADC.
also needs
- Bleed air - which is taken from the engines for air conditioning,
• Anti ice,
• Pneumatic loads - various.
