Systems Review 3 ATC Chapter 4

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

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

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

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.

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

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

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

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

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.

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

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

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

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

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)

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

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

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

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

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

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

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

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

2. System failures Pitot Static System

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

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

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

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

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

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

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

Questions?