Automatic Flight Control (Autopilot)

Question 1

What are the various autopilot modes of operation?

Answer 1

SAS Modes
Cruise Mode
Launch and Recovery Mode
Hold Modes (heading, airspeed, altitude)
Airspeed Limit Override
Speed Priority Override
Aileron Tipstall Override
Stall Protect
Roll Limit Override
Sideslip Protect
Preprogram Flight Mode (operational & emergency mission)
Lost Link Logic

Question 2

Describe SAS Mode

Answer 2

SAS = Stability Augmentation System = ensures control commands are within aircraft flight envelope

SAS ON = autopilot attempts to maintain the attitude commanded by the control stick

SAS should only be turned off for ground maintenance or inflight emergencies. Aircraft handling is completely different and any input will cause aircraft to continue to change attitude. Also, turning off SAS deactivates all autopilot safety features

Question 3

Describe Cruise Mode

Answer 3

Reduces/limits control sensitivity and travel based on airspeed and activates roll limit override

Activates when any of the following conditions are met:
-Any hold mode is engaged (except RPM Hold)
-Stall protect is enabled
-Airspeed is >110 KIAS

Turns off as aircraft decelerates below 100 KIAS with stall protect off and all hold modes off

Question 4

Describe Launch and Recovery Mode

Answer 4

Aircraft is in this mode when ALL the following are true:
-Any hold mode on
-Stall protect disabled
-Airspeed <100 KIAS

Question 5

What are the hold modes? Considerations with those modes?

Answer 5

Heading
Airspeed
Altitude

SAS should be on before activating a hold mode

Do not attempt to land with a hold mode engaged because of limited control

Question 6

Describe Heading Hold Mode

Answer 6

Heading hold feature to maintain commanded magnetic heading

Autopilot will turn aircraft the shortest distance to the new heading

Angle of bank depends on link type
LOS = 30 degree bank
Ku = 14 degrees of bank

Question 7

Describe Airspeed Hold Mode

Answer 7

Autopilot maintains a commanded airspeed

Minimum is determined by Vs x 1.06 and even though you can command an airspeed slower airspeed limit override will set it to minimum rather than commanded
Maximum is 200 KIAS but limited by software to 190 KIAS (airspeed hold only) or 180 KIAS (airspeed and altitude hold)

Question 8

Describe Airspeed Limit Override

Answer 8

Activated when airspeed hold is on

Prevents the pilot from setting an airspeed hold value that is less than Vs x 1.06

Question 9

Should you zero pitch and roll trims in flight?

Answer 9

No! Abrupt changes in flight control can occur and cause structural failure or departure from controlled flight

Question 10

Describe Altitude Hold Mode

Answer 10

Maintains a commanded altitude

Airspeed hold must be engaged before selecting altitude hold (turning off airspeed hold will also turn off altitude hold)

Automatically turns on closed loop power because throttle is automatically controlled to maintain altitude

Aircraft performance dictated by airspeed preference or altitude preference mode

You can set an altitude lower than the minimum MSL altitude preset, but aircraft will not descent below minimum MSL altitude

Climbs are done at best climb airspeed >1,200’ and commanded airspeed <1,200’
Descents are done at airspeed hold or mission parameters

Question 11

What is the difference between airspeed preference and altitude preference?

Answer 11

Pitch is used to control whatever mode has preference

Airspeed preference = less than Vs x 1.12 + 10 KIAS
Altitude preference = more than Vs x 1.12 + 10 KIAS

Question 12

Describe Speed Priority Override

Answer 12

Additional stall protection when aircraft is in altitude preference mode (normal indication during a long climb in altitude preference mode)

Activated when airspeed is less than Vs x 1.12

Performs the following:
-Pitch controls airspeed
-Airspeed set to best climb airspeed
-“Best Climb Speed Override” displayed on HUD

Question 13

Describe Aileron Tipstall Override

Answer 13

First level of stall protect
Automatically decambers ailerons when AOA increases above 5 degrees
At 9 degree AOA deflects ailerons to maximum -8 degree

Automatically enabled

Automatically disabled when:
-Airspeed <50 or >134 KIAS
-ATLC land active and UAV past WP4
-ATLC takeoff active and UAV <300’ AGL

Question 14

Describe Stall Protect

Answer 14

Limits aircraft AOA to prevent stall
When AOA exceeds 7 degrees pitches the nose down and limits roll until AOA is less than 3 degrees

Turned on and off by the pilot (usually <2,000’ AGL) but only takes effect at speeds below 120 KIAS (automatically disabled >120 KIAS)

Turning stall protect on also automatically turns on cruise mode

Question 15

Describe Roll Limit Override

Answer 15

Uses Cl 1.25 to maintain a safety margin between the aircraft airspeed and stall speed due to roll angle (accelerated stall)

Automatically activated if any of the following:
-Any hold mode on (airspeed, altitude, heading)
-LOS link mode

If pilot commands a roll angle that exceeds limit the bank angle is overridden and a message “Roll Limit Override” on HUD

Aircraft will limit bank and will pitch down as necessary to maintain safety margin for increased stall speed due to bank angle

Question 16

Describe Sideslip Protect Mode

Answer 16

Always enabled

Automatically adjusts rudder to keep the aircraft coordinated in a turn

Question 17

Describe waypoint turn logic

Answer 17

Normal waypoint = logic is based on turn basket (caution - some waypoints can be skipped if groundspeed and roll limits determine waypoint is too close or has already completed waypoint. When waypoint is skipped aircraft looks for the following waypoint and might turn the “opposite direction” because it turns in the direction of least course change)

Flyover waypoint = flys over waypoint before turning

Question 18

What does landing configuration command turn off?

Answer 18

All hold modes
Stall protect
Preprogram mode

Question 19

What is the difference between landing configuration and pilot takeover?

Answer 19

Pilot takeover = disables ATLC
landing configuration = disables hold modes, stall protect, and preprogram mode

Question 20

Describe Dive Priority Override

Answer 20

Aircraft will bring torque to 0% and use pitch to keep airspeed from exceeding Vne (keeps airspeed <Vne -5)

Note: only limiting airspeed (no limitation for Vle or Vlo or Vfe)