1. Systems Review 3
ATC Chapter 4

2. Aim
To review principals of operation of pressure, gyroscopic and electrical instruments

3. Objectives
State what each instrument indicates and name the power source for each instrument
State the effect of system failures on instrument indications

4. 1. Instruments indications and source
Artificial Horizon (AH or AI)
Sometimes referred to as the master instrument
Indicates both pitch and bank attitude directly (in miniature) against the artificial horizon
Miniaturization of the outside world means that small movements of the AH represent quite large changes in pitch and bank attitudes
Indirectly, the AH is a guide to airspeed
Nose low, high or increasing airspeed
Nose high, low or decreasing airspeed
Most commonly driven by an engine driven vacuum pump but can be electrically driven or venturi driven

5. 1. Instruments indications and source
Airspeed indicator (ASI)
Directly indicates the aircrafts speed through the air by measuring the difference between total pressure from the Pitot tube and the static pressure from the static source
Total pressure – Static pressure = Dynamic pressure
Indirectly indicates the pitch attitude of the aircraft
Low or decreasing airspeed, nose high
High or increasing airspeed, nose low
The ASI is driven by the Pitot static system and requires both dynamic and static pressure.

6. 1. Instruments indications and source
Altimeter
Directly indicates the aircrafts height above a datum
In Australia below 10,000ft AMSL seal level is set as the datum
Indirectly indicates pitch attitude
Altitude decreasing, nose low
Altitude increasing, nose high
The altimeter is driven by the aircrafts static vent

7. 1. Instruments indications and source
Altimeter – Incorrect subscale settings
Below 5,000ft every 1 hPa that the altimeter is in error is equal to 30ft error displayed on the altimeter
If the subscale is set too low the altimeter will read low
If the subscale is set too high the altimeter will read high

8. 1. Instruments indications and source
Vertical Speed Indicator (VSI)
Directly indicates the rate of change of altitude.
Indirectly it indicates pitch attitude
VSI decreasing, nose low
VSI increasing, nose high
Useful as a trend indicator
The vertical speed indicator is driven by the aircrafts static vent

9. 1. Instruments indications and source
Heading Indicator
Allows direct reading of heading
Can be a Direction Gyro (DG) or Horizontal Situation Indicator (HSI)
DG must be manually aligned with aircraft compass. HSI automatically aligns with the Earths magnetic field
Indirectly it indicates Bank angle
HSI decreasing, left turn
HSI increasing, right turn
Electronically driven or driven by vacuum pump

10. 1. Instruments indications and source
Turn Coordinator (TC)
Directly indicates the rate of change of direction
Indirectly it can indicate limited angles of bank usually to 35 degrees
Usually powered by an electrically driven Gyro.

11. 3. Instrument Indications
1. Instruments indications and source
3. Instrument Indications
Balance Indicator
Directly indicates balance
Usually incorporated with the turn co-ordinator
Indirectly indicates aircraft yaw
Powered by gravity
Slipping Turn
Skidding Turn
Co-ordinated Turn

12. 1. Instruments indications and source
Tachometer
Directly indicates engine RPM
Indirectly indicates pitch in aircraft without a CSU
Increase RPM, nose low
Decrease RPM, nose high
Driven by the engine via mechanical linkage

13. 1. Instruments indications and source
Magnetic Compass
Allows direct reading of heading
Primary navigation aid for most light aircraft
Indirectly it indicates Bank angle
Compass decreasing, left turn
Compass increasing, right turn
Susceptible to a number of errors

14. 1. Instruments indications and source
Magnetic Compass
Reading the compass
When we look at the compass we are reading the back of it. This means the compass in our aircraft reads backwards
This is best shown on a boat compass. If we are heading 300 and wanted to turn onto 270 we know the shortest turn will be to the left.
When we are looking top down on the compass we can see 270 is to the left of 300. However when we look at the front of the compass card 270 is to the right of 300

15. 1. Instruments indications and source
Magnetic Compass
Variation
Angular difference between true north and magnetic north
The magnet in the compass aligns itself with the earths lines of magnetic flux (magnetic north)

16. 1. Instruments indications and source
Magnetic Compass
Deviation
Occurs when the compass magnet is acted upon by a magnetic field other than the Earths. Can be caused by electronic or metal objects near the compass.
The error is displayed on a compass deviation card produced by an engineer after they carry out a compass swing

17. 1. Instruments indications and source
Magnetic Compass
Dip
At the equator the earths magnetic field is parallel with the earths surface, the magnetic bar of the compass also lies parallel with the Earths surface

18. 1. Instruments indications and source
Magnetic Compass
Dip
As you travel closer to the poles the lines of magnetic flux begin to dip, so to does the magnetic bar of the compass
To help reduce this error the compass magnet is suspended from a pivot point.
This now means the center of gravity of the compass magnet is always going to be displaced from the pivot point

19. 1. Instruments indications and source
Magnetic Compass
Turning Errors
Because the center of gravity of the magnet is displaced from the pivot point, when we Bank the aircraft there is a horizontal component of gravity that acts on the compass resulting in a change of heading indicated
This error is maximum on North and South, nil on East or West
To remember which way it will rotate we use the acronym ONUS O N U S
vershoot
orth
ndershoot
outh

20. 1. Instruments indications and source
Magnetic Compass
Acceleration Errors
Because the center of gravity of the magnet is displaced from the pivot point, when we accelerate or decelerate the compass will lag behind the aircraft and will rotate. This error is maximum on East or West, nil on North or South
When we accelerate the compass will swing towards the south, when we decelerate the compass will swing towards the north
To remember which way it will rotate we use the acronym SAND S A N D
outh
ccelerate
orth
ecelerate

21. 1. Instruments indications and source
G1000
Directly indicates all of the above parameters
Information is generated by the air data computer, AHRS and magnetometer
All indications are displayed on the PFD and MFD

22. 2. System failures Vacuum Failure Instruments affected
Artificial horizon
Direction Gyro
Indicated by:
low VAC pressure reading
Annunciator
Troubleshooted by:
Can get false indications at low RPM

23. 2. System failures Vacuum Failure Artificial Horizon
Failure indicted by:
The gyro toppling, may happen over an extended period of time as the gyro slows down
Red warning flag
Direction Gyro
Failure indicted by:
Red warning flag
Inaccurate readings, check against compass

24. 2. System failures
Pitot Static System

25. 2. System failures Pitot Blockage Instruments affected
Airspeed indicator
Indicated by:
No airspeed increase during takeoff roll
Troubleshooted by:
If failure is identified during the takeoff roll abort the takeoff if it is safe to do so
If failure occurs airborne Pitot heat may be required, refer to flight manual

26. 2. System failures Pitot Blockage Airspeed Indicator
Failure indicted by:
No airspeed increase during take off roll
If Pitot tube blockage occurs during flight the ASI is only read correctly at blockage altitude
If aircraft climbs above blockage height ASI over-reads
If aircraft descends below blockage height ASI under-reads

27. 2. System failures Static Blockage Instruments affected
Airspeed indicator
Altimeter
Vertical speed indicator
Indicated by:
ASI over or under reading
Altimeter not increasing with an increase in altitude
VSI reading zero with an increase in altitude
Troubleshooted by:
Alternate static source may be required, refer to flight manual

28. 2. System failures Static Blockage Airspeed Indicator
Failure indicted by:
If static source blockage occurs during flight the ASI is only correct at blockage altitude
If aircraft climbs above blockage height ASI under-reads
If aircraft descends below blockage height ASI over-reads

29. 2. System failures Static Blockage Altimeter Failure indicted by:
Will continue to read blockage altitude with an increase or decrease in altitude
Vertical Speed Indicator
Failure indicted by:
Will continue to read zero with an increase or decrease in altitude

30. 2. System failures Electrical Failure Instruments affected G1000
Turn coordinator
Indicated by:
Very high voltage reading
Very low voltage reading
Very high amp reading
Very low amp reading
Annunciator
Troubleshooted by:
Depends on indication, refer to flight manual

31. 2. System failures Electrical Failure G1000 Failure indicted by:
Red X through affected instruments
If complete failure occurs the screens may cease to function
Turn coordinator
Failure indicted by:
Red warning flag
Note: The balance ball will still be functional

32. Questions?