Flight Instruments

Question 1

Static Pressure of Atmosphere

Answer 1

• Pressure of atmosphere
• Static Port

Question 2

Total Pressure

Answer 2

• Pressure created inside the pitot tube as the aircraft moves forward
• Includes both static pressure and pressure increase due to forward motion of aircraft

Question 3

Dynamic Pressure

Answer 3

• Pressure difference between total pressure and static pressure
• Direct indication of forward speed of aircraft

Question 4

Density Altitude

Answer 4

Pressure Altitude corrected for non-standard temperature

Question 5

True Altitude

Answer 5

Exact Altitude above sea level

Question 6

Absolute Altitude

Answer 6

Exact Altitude above ground level

Question 7

Altimeter Operation

Answer 7

• When altitude increases, static pressure decreases, capsule expands, gears convert expansion to needle movement up
• sub scale knob used to correct for high and low pressure air (28”Hg - 31”Hg)
• Should not be more than +/- 50 feet of elevation when on ground

Question 8

Altimeter Position Error

Answer 8

Static port senses dynamic pressure during slips, causing altimeter error

Question 9

Altimeter Scale Error

Answer 9

• Aneroids not assuming precise size of pressure difference
• Increases with altitude

Question 10

Altimeter Mechanical Error

Answer 10

Caused by misalignment or slippage in gears

Question 11

Altimeter Density Error

Answer 11

• Caused by variations in atmospheric pressures and temperatures
• 1’’ Hg error = 1000’ ft error
• High to low, lookout below (altimeter over-reading)
• Low to high, clear blue sky (altimeter under-reading)

Question 12

Altimeter Hysteresis Error

Answer 12

A lag in indications due to elastic properties of the materials used to construct aneroids

Question 13

Altimeter Reversal Error

Answer 13

• Caused by rapid or abrupt attitude changes
• only momentary in duration

Question 14

Vertical Speed Indicator (VSI) Operation

Answer 14

• When altitude increases, static pressure decreases, capsule contracts, gears convert contraction to needle movement up
• VSI returns to 0 when pressure in case matches pressure in diaphragm
• Should be inspected if showing greater than 100 fpm on the ground

Question 15

VSI Lag Error

Answer 15

• VSI lags 6-9 seconds to settle on a rate due to calibrated leak which is connected to the static source
• Shows trends immediately
• smoother transitions produce less lag
• Instantaneous VSI’s have accelerometers that move the pointer until diaphragm takes over

Question 16

Calibrated Airspeed

Answer 16

Indicated airspeed corrected for instrument and position error

Question 17

Equivalent Airspeed

Answer 17

Calibrated Airspeed corrected for compressibility factor

Question 18

Airspeed Indicator Operation

Answer 18

• Measures difference between total pressure (pitot tube) and static pressure (static port) to get dynamic pressure
• Dynamic pressure is a direct indication of airspeed

Question 19

Airspeed Density Error

Answer 19

• Since static pressure decreases with altitude, total pressure will also decrease
• This means TAS will be higher than IAS
• Increase IAS 2% for each 1000ft to obtain TAS

Question 20

Airspeed Instrument Error

Answer 20

Caused by mechanical errors present within the instrument

Question 21

Hysteresis Error

Answer 21

Lag in indications due to elastic properties of aneroids

Question 22

Airspeed Position Error

Answer 22

• Airframe disturbing airflow around pitot tube or static port
• Example is high angle of attack
• CAS corrects this

Question 23

Pitot Source Blocked

Answer 23

• Airspeed Indicator = increasing in climb / decreasing in descent
• Altimeter = unaffected
• VSI = unaffected

Question 24

One Static Source Blocked

Answer 24

All are inaccurate while slipping and very sensitive in turbulence

Question 25

Both Static Sources Blocked

Answer 25

- Airspeed Indicator = decreasing in climb / increasing in descent - Altimeter = Freezes - VSI = Reads 0

Question 26

Both Static and Pitot Sources Blocked

Answer 26

- Airspeed Indicator = Freezes - Altimeter = Freezes - VSI = Reads 0

Question 27

Pitot Source Partially Blocked

Answer 27

- Airspeed Indicator =Reads 0 - Altimeter and VSI unaffected

Question 28

Static Source Partially Blocked

Answer 28

- All will under read in a climb and catch up after levelling off - All will over read in a descent and catch up after levelling off

Question 29

Attitude Indicator Operation

Answer 29

- Gyro Mounted Horizontally and spins about a vertical axis - Usually Vacuum driven - Functions on principle of rigidity in space - Linkages transfer movements around gyro to artificial horizon face - Should be stable while taxiing - Limitations are 85 degrees of bank and pitch

Question 30

Heading Indicator Operation

Answer 30

- Gyro Mounted Vertically and Spins Horizontally - Usually vacuum driven - Functions on principle of rigidity in space - Linkages transfer movements around gyro to heading indicator face - Excessive precession indicates that the gyro is worn - Limitations are 85 degrees of bank and pitch

Question 31

Mechanical Precession Heading Indicator Error

Answer 31

- Frictional forces cause gyro to precess - Causes gyro instruments to drift 3º every 15 minutes - Reset heading indicator every 15 minutes

Question 32

Apparent Precession Heading Indicator Error

Answer 32

- Earth rotates under the gyro - Heading appears to precess depending on latitude - zero at the equator, 15 degrees an hour at the poles - Corrected by resetting every 15 minutes

Question 33

Turn and Slip Operation

Answer 33

- Provides direction and rate of turn, as well as coordination - Gyro Mounted Vertically and Spins Horizontally - Electrically Driven - Functions on principle of gyroscopic precession - Needle only sensitive to yaw, not roll

Question 34

Rate One Turn

Answer 34

- On L or R in turn and slip or turn coordinator - 180º per minute

Question 35

Turn Coordinator Operation

Answer 35

- Gyro Mounted Vertically and Spins Horizontally - Canted at 35 degree angle - Usually electrically driven - Functions on principle of gyroscopic precession - Sensitive to roll as well as yaw

Question 36

Magnetic Compass Operation

Answer 36

- Mounted on a pivot and free to rotate within bowl of kerosene - Should be free and swinging during turns on the ground - Limited to 20º of pitch - Unreliable in NDA due to magnetic dip

Question 37

Variation

Answer 37

- Difference between magnetic north and true north - Add westerly track / subtract easterly track to true track to get magnetic track

Question 38

Acceleration Compass Errors

Answer 38

- Causes a turning error - ANDS (Accelerate North Decelerate South) - Error does not exist on north and south headings

Question 39

Turning Compass Errors

Answer 39

- Causes an acceleration error - SAND (South Advance North Delay) - Error does not exist on east and west headings