1. AUTOMATIC FLIGHT CONTROL SYSTEM (AFCS)

2. PURPOSE: To develop the Student
Instructor Pilot’s understanding of the
Automatic Flight Control System
NEED: You will be instructing this
subject in the near future

3. TOPICS OF DISCUSSION Auto Flight Control System What is Stability?
Stability Augmentation System
TRIM
Flight Path Stabilization
Malfunction Analysis

4. WHAT IS AFCS?
AFCS enhances the stability and handling qualities of the UH60 helicopter. It is comprised of four subsystems:
Stability Augmentation System (SAS)
Trim Systems
Flight Path Stabilization (FPS)
Stabilator (previously discussed)

6. WHAT IS STABILITY?

7. Stability, in physics and engineering, the property of a body that causes it to return to its original position or motion as a result of the action of the so-called restoring forces, or torques, once the body has been disturbed from a condition of equilibrium or steady motion.

8. STABILITY AUGMENTATION SYSTEM (SAS)
Purpose: Provide dynamic stability through short term rate dampening in the pitch, roll, and yaw axis.
SAS systems: SAS 1 & SAS 2
Control Authority: Each SAS has 5% control authority, for a total of 10%
If one SAS is turned off or inop, the other SAS doubles its gain but still only has 5% control authority.

9. SAS 1 Components: Input Signals:
SAS1 amplifier (analog) is located in the avionics compartment
Three SAS actuators
Input Signals:
Pitch - rate gyro in the #1 stabilator amplifier
Roll - pilot’s (number 2) vertical gyro
Yaw - yaw rate gyro in the SAS1 amplifier
additional signals - #1 filtered lateral accelerometer, airspeed transducer

10. #1 pitch rate gyro #2 vertical gyro #1 lateral accl a/s transducer
Yaw gyro
#1 pitch rate gyro
#2 vertical gyro
#1 lateral accl
a/s transducer

11. SAS 2 Components: Input Signals:
SAS2 is the SAS/FPS computer (digital)
Three SAS actuators
Input Signals:
Pitch - rate gyro in the #2 stabilator amplifier
Roll - roll rate gyro in the avionics compartment
Yaw - yaw rate gyro in the avionics compartment

12. SAS 2 Additional Signals #1 & #2 filtered lateral accelerometer
rate gyro in the #1 Stabilator amplifier
air data transducer

13. Yaw rate gyro
#1 & #2 lateral accl
Air data transducer
Roll rate gyro
#2 pitch rate gyro

14. TRIM SYSTEM
Purpose: Provide a gradient force, maintains position of the cyclic and tail rotor controls
Components:
two electromechanical actuators, and one electrohydromechanical actuator
TRIM REL switch on the cyclic, and pedal micro switches on the directional control pedals
monitored by the SAS/FPS computer

15. Yaw Trim
Proper operation requires that the Boost be on and pressurized.
Electromechanical actuator that incorporates a slip clutch in the event the actuator jams. (80 lbs)
Trim/FPS hardover will result in 1/4 inch pedal movement
Reference is changed by pressing micro switches on the pedals and release.

16. Roll Trim
Electromechanical actuator with slip clutch. Force required to override the clutch is 13 lbs.
Located on the cabin top under the control access.
Roll Trim/FPS hardover will result in 1/2 inch cyclic displacement.
Reference is reset using the trim release switch or stick trim switch.

17. Pitch Trim
Hydroelectromechanical actuator that operates in conjunction with the SAS/FPS computer.
Located on the cabin top above the pitch boost servo.
Hydraulic pressure is 1000 lbs.
Pitch Trim/FPS hardover results in about 1/2 inch cyclic displacement.

18. Airspeed transducer
#1 collective position sensors

19. FLIGHT PATH STABILIZATION
Purpose: Enhances static stability through long term rate dampening in the pitch, roll, and yaw axis.
Components: SAS/FPS computer, and three trim actuators
Control Authority: When coupled with trim, 100% control authority

20. FLIGHT PATH STABILIZATION
The following systems must be on and operational for FPS to function 100%
SAS 1 and/or SAS 2
Boost
Trim
Stabilator in AUTO mode enhances FPS operation, but is not required

21. FLIGHT PATH STABILIZATION
FPS provides the following functions:
BELOW
60 KIAS
ABOVE
Attitude Hold/
Airspeed Hold
Attitude Hold
Pitch Axis
Attitude Hold
Roll Axis
Attitude Hold
Heading Hold or
Turn Coordination
Heading Hold
Yaw Axis

22. Airspeed transducer
#1 collective position sensor
#1 pitch rate gyro
#1 vertical gyro
#1 vertical gyro
ASN 43
#1 lateral accl
Airspeed transducer
#1 collective position sensor

23. MALFUNCTION ANALYSIS

24. ON ON ON ON ON ON AUTO FLIGHT CONTROL SAS 1 SAS 2 TRIM FPS BOOST
FAILURE
ADVISORY
RESET
RESET ON ON
POWER ON RESET

25.  SAS 1 and FPS switchs - Off.
SAS Failure With No Failure/Advisory Indication.
 SAS 1 switch - Off.
If condition persists:
 SAS 1 switch - On.
 SAS 2 switch - Off.
If malfunction still persists:
 SAS 1 and FPS switchs - Off.

26. ON ON ON ON ON ON AUTO FLIGHT CONTROL SAS 1 SAS 2 TRIM FPS BOOST
FAILURE
ADVISORY
RESET
RESET
SAS2 ON ON
POWER ON RESET

27. 9.29.2 SAS2 Failure Advisory Light On.
Power On Reset switches - Simultaneously press and then release.

28. ON ON ON ON ON ON AUTO FLIGHT CONTROL SAS OFF SAS 1 SAS 2 TRIM FPS
BOOST
FAILURE
ADVISORY
RESET
RESET ON ON
POWER ON RESET

29. 9.29.3 SAS OFF Caution Light On.
FPS switch - Off.

30. ON ON ON ON ON ON AUTO FLIGHT CONTROL SAS OFF SAS 1 SAS 2 TRIM FPS
BOOST
FAILURE
ADVISORY
RESET
RESET ON ON
POWER ON RESET

31. ON ON ON ON ON ON AUTO FLIGHT CONTROL FLT PATH STAB SAS 1 SAS 2 TRIM
FPS ON ON ON ON
BOOST
FAILURE
ADVISORY
RESET
RESET ON ON
A /S
POWER ON RESET

32. 9.29.4 FLT PATH STAB Caution Light On.
 POWER ON RESET switches - Simultaneously press and then release.
WARNING
If the airspeed fault advisory light is illuminated, continued flight above 70 KIAS with the stabilator in the AUTO MODE is unsafe since a loss of the airspeed signal from the remaining airspeed sensor would result in the stabilator slewing full down.

33. 9.29.5 Pitch, Roll or Yaw/Trim Hardover.
POWER ON RESET switches - Simultaneously press and then release.
If failure returns, control affected axis manually.

34. LAND AS SOON AS PRACTICABLE.
Trim Actuator Jammed.
LAND AS SOON AS PRACTICABLE.