Autopilot Flashcards
What is the difference between inner loop and outer loop?
inner loop systems provide the controls, outer loop systems provide the data which will ‘close the loop’. I.e. altitude not held (detected by outer loop), inner loop is closed and causes controls to fix deviation.
What do rate dampeners and torque limiters do?
Assist the feedback comparator signal to prevent autopilot runaways
What movement does a single axis autopilot control?
Roll (lateral stabilisation)
What movement does a ‘two axis’ autopilot control?
Roll and pitch (lateral and longitudinal stabilisation)
What movement does a ‘three axis’ autopilot control?
Roll, pitch, yaw.
How many inner loops will an autopilot system have?
An amount equal to the amount of axes controlled. single axis = 1, two axis = 2, 3 axis = 3.
How many autopilots do most large aircraft typically have?
2 or 3, the purpose of this is for redundancy and cross-checking
What is the CADC?
Central Air Data Computer: Receives manometric data from the pitot static system and TAT. Can calculate IAS, TAS, Mach #, and pressure altitude.
How does the CADC use data for the autopilot?
Converts pressure signals to electrical signals
What phases of flight can the autothrottle be engaged in?
All stages
What is used to control airspeed during a climb or descent, attitude or throttles?
Attitude (power remains constant)
What is used to control airspeed, attitude or power?
Power. Though attitude is also changed to maintain correct power + attitude.
When operating on autopilot on a VOR, what does the system do once the cone of confusion is entered?
reverts to HDG hold mode, until signal returns again.
What is CWS (Control Wheel Steering)?
Allows the pilot to manually control the aircraft without disengaging to autopilot. Once the CWS is released, the AP will hold the now AoB or Attitude.
What is the difference between series-connected and parallel connected servomotors in an autopilot system?
In series, the pilot’s controls don’t move.
In parallel, the pilot’s controls move. (DA40 has parallel)
What is the purpose of the torque limiter?
Prevents the controls being deflected too strongly (AP can’t ‘feel), so will disengage the servomotors is a certain threshold is exceeded.
What is autopilot hardover, and how is it managed?
Tendency for autopilot to use FULL deflection. Prevented by the torque limiter.
How many autopilots are required for autoland?
2
What are the two types of autoland systems? Explain.
Fail passive (soft): In the event of a system failure, the flight path will be maintained, but the autolanding will not be done. Fail operational. If a failure of one AP occurs, the landing will still be completed because it just turns into a fully functional 'fail passive system'.
How many autopilots does a fail passive system have?
- This is why the approach must be manually flown in the event of a failure, because autoland cannot be done with one autopilot.
How many autopilots does a fail operational system have?
- If one of the autopilots fails, it simply reverts to ‘fail passive’ mode.
What are the three ‘fail operational’ settings?
Land 3: indicates 3 channels are engaged.
Land 2: Indicates 2 channels are engaged, therefore reverts to a ‘fail passive’ system.
No autoland: Only 1 channel available, therefore autoland not possible.
In the event of 1 channel failing in a fail passive system, what will happen?
warnings displayed to the pilot, and autopilot will disengage itself at 350ft RADALT.
At what altitude does a RADALT become active?
2500ft
At what altitude is the flare and rollout of an autoland system ARMED (not engaged)
1500ft
At what altitude during an autoland approach, is the stabiliser trim engaged to pitch nose up?
330ft
At what height during an autoland is flare mode automatically engaged?
50ft. RoD is then done at 2ft/second
At what altitude during the autoland is the rollout engaged?
5ft.
What type of autoland does the B767 have?
Fail operational (3 autopilots)
What systems comprise the Automatic Flight System?
AFDS (Autopilot Flight Director System), and A/T (Auto Throttle)
How do the pilots know what the status of the Automatic Flight System
Displayed on each pilot’s EFIS ADI. Engaged modes are green for 10 seconds, armed modes are in white and are displayed under the engaged modes.
What is Takeoff Mode?
Maintains wings level after takeoff (typically up to 400ft).
What is Go-Around mode?
Maintains runway track during a missed approach (typically up to 400ft).
How does Cost Index work?
Programmed into the FMC to dictate if best speed or economy is preferred. High values dictate high economy (max number 999), low numbers indicate good economy.
When VNAV is engages and a SID or STAR is being flown, will the aircraft maintain speed limitations on the plate?
Yes, they are automatically programmed.
VNAV takes data from both the MCP and the FMC, how does the pilot know what data is being used?
Typically the MCP windows will be masked when FMC data is being used (e.g. speed during a STAR).
What is a Drag Required message?
Prompts the crew to extend the speedbrakes. Note that the system will deviate from the desired path if it means maintaining the speed….
What is Flight Level Change (FLCH) mode?
When climbing or descending, the pitch mode annunciation is replaced by SPD, and the autothrottle mode replaced by FLCH.
What happens at level-off from FLCH mode?
The pitch mode changes from SPD to ALT CAP, then ALT hold. The Autothrottle changes from FLCH to SPD.
At what altitude are pilots notified that they are approach their level off altitude?
900ft, indicated on their altimeters.
When will an ALT alert message be displayed?
When the altitude deviation is 300ft
When would you use VS instead of FLCH?
FLCH uses max RoD/RoC, but VS can be used for a gentle rate of descent
What indications are associated with FLARE mode engaging?
Autothrottles reducing to idle, A/T indicating IDLE instead of SPD
With autoland, how long are the throttles kept at flight idle before ground idle, and why?
5 seconds. This is to facilitate better response time for reverse thrust or go-around
If an engine fails during takeoff, is there a requirement to increase thrust?
No, the thrust set for takeoff will meet all performance requirements.
What is the relationship between thrust and pitch for autopilots?
only one can control IAS at any time. In a climb, it’s controlled by pitch, in cruise, it is controlled by thrust.
