Systems Review 3 ATC Chapter 4. Aim To review principals of operation of pressure, gyroscopic and electrical instruments

Systems Review 3ATC Chapter 4

Aim

To review principals of operation of pressure, gyroscopic and electrical instruments

Objectives1. State what each instrument indicates and name

the power source for each instrument2. State the effect of system failures on instrument

indications

Artificial Horizon (AH or AI)Sometimes referred to as the master instrument

Indirectly, the AH is a guide to airspeed• Nose low, high or increasing airspeed• Nose high, low or decreasing airspeed

Miniaturization of the outside world means that small movements of the AH represent quite large changes in pitch and bank attitudes

Indicates both pitch and bank attitude directly (in miniature) against the artificial horizon

Most commonly driven by an engine driven vacuum pump but can be electrically driven or venturi driven

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

The ASI is driven by the Pitot static system and requires both dynamic and static pressure.

Indirectly indicates the pitch attitude of the aircraft• Low or decreasing airspeed, nose

high• High or increasing airspeed, nose

low

Total pressure – Static pressure = Dynamic pressure


AltimeterDirectly indicates the aircrafts height above a datumIn Australia below 10,000ft AMSL seal level is set as the datum

The altimeter is driven by the aircrafts static vent

Indirectly indicates pitch attitude• Altitude decreasing, nose low• Altitude increasing, nose high


Altimeter – Incorrect subscale settingsBelow 5,000ft every 1 hPa that the altimeter is in error is equal to 30ft error displayed on the altimeterIf the subscale is set too low the altimeter will read lowIf the subscale is set too high the altimeter will read high


Vertical Speed Indicator (VSI)Directly indicates the rate of change of altitude.

The vertical speed indicator is driven by the aircrafts static vent

Indirectly it indicates pitch attitude• VSI decreasing, nose low• VSI increasing, nose high

Useful as a trend indicator


Heading Indicator

Can be a Direction Gyro (DG) or Horizontal Situation Indicator (HSI)

Electronically driven or driven by vacuum pump

Indirectly it indicates Bank angle• HSI decreasing, left turn• HSI increasing, right turn

DG must be manually aligned with aircraft compass. HSI automatically aligns with the Earths magnetic field

Allows direct reading of heading


Turn Coordinator (TC)

Usually powered by an electrically driven Gyro.

Indirectly it can indicate limited angles of bank usually to 35 degrees

Directly indicates the rate of change of direction


3. Instrument IndicationsBalance Indicator

Powered by gravity

Indirectly indicates aircraft yaw

Directly indicates balance

Usually incorporated with the turn co-ordinator

Slipping Turn Skidding Turn Co-ordinated Turn


Tachometer

Driven by the engine via mechanical linkage

Indirectly indicates pitch in aircraft without a CSU• Increase RPM, nose low• Decrease RPM, nose high

Directly indicates engine RPM


Primary navigation aid for most light aircraft

Magnetic Compass

Indirectly it indicates Bank angle• Compass decreasing, left turn• Compass increasing, right turn

Allows direct reading of heading

Susceptible to a number of errors


When we look at the compass we are reading the back of it. This means the compass in our aircraft reads backwards

Magnetic CompassReading the compass

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


Angular difference between true north and magnetic north

Magnetic CompassVariation

The magnet in the compass aligns itself with the earths lines of magnetic flux (magnetic north)


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.

Magnetic CompassDeviation

The error is displayed on a compass deviation card produced by an engineer after they carry out a compass swing


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

Magnetic CompassDip


Magnetic CompassDipAs 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


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

Magnetic CompassTurning Errors

To remember which way it will rotate we use the acronym ONUS

ONUS

vershootorth

outhndershoot

This error is maximum on North and South, nil on East or West


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

Magnetic CompassAcceleration Errors

SAND

outhccelerate

ecelerateorth

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


G1000

Information is generated by the air data computer, AHRS and magnetometer

Directly indicates all of the above parameters

All indications are displayed on the PFD and MFD


• Artificial horizon• Direction Gyro

Vacuum FailureInstruments affected

Indicated by:

Troubleshooted by:

• low VAC pressure reading• Annunciator

• Can get false indications at low RPM

2. System failures

Vacuum FailureArtificial 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

• Red warning flag• Inaccurate readings, check against compass

Failure indicted by:

2. System failures

Pitot Static System2. System failures

• Airspeed indicator

Pitot BlockageInstruments affected

Indicated by:

Troubleshooted by:

• No airspeed increase during takeoff roll

• 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

2. System failures

Pitot BlockageAirspeed 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

2. System failures

• Airspeed indicator• Altimeter• Vertical speed indicator

Static BlockageInstruments affected

Indicated by:

Troubleshooted by:

• ASI over or under reading• Altimeter not increasing with an increase in altitude• VSI reading zero with an increase in altitude

• Alternate static source may be required, refer to flight manual

2. System failures

Static BlockageAirspeed 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

2. System failures

Static BlockageAltimeter

Failure indicted by:• Will continue to read blockage altitude

with an increase or decrease in altitude

Vertical Speed Indicator


• Will continue to read zero with an increase or decrease in altitude

2. System failures

• G1000• Turn coordinator

Electrical FailureInstruments affected

Indicated by:

Troubleshooted by:

• Very high voltage reading• Very low voltage reading• Very high amp reading• Very low amp reading• Annunciator

• Depends on indication, refer to flight manual

2. System failures

Electrical FailureG1000

Failure indicted by:• Red X through affected instruments• If complete failure occurs the screens

may cease to function

Turn coordinator

• Red warning flag


Note: The balance ball will still be functional

2. System failures

Questions?

Documents

Systems Review 3 ATC Chapter 4. Aim To review principals of operation of pressure, gyroscopic and electrical instruments