Flight Instruments Flashcards
1
Q
Static Pressure of Atmosphere
A
- Pressure of atmosphere
- Static Port
2
Q
Total Pressure
A
- Pressure created inside the pitot tube as the aircraft moves forward
- Includes both static pressure and pressure increase due to forward motion of aircraft
3
Q
Dynamic Pressure
A
- Pressure difference between total pressure and static pressure
- Direct indication of forward speed of aircraft
4
Q
Density Altitude
A
Pressure Altitude corrected for non-standard temperature
5
Q
True Altitude
A
Exact Altitude above sea level
6
Q
Absolute Altitude
A
Exact Altitude above ground level
7
Q
Altimeter Operation
A
- 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
8
Q
Altimeter Position Error
A
Static port senses dynamic pressure during slips, causing altimeter error
9
Q
Altimeter Scale Error
A
- Aneroids not assuming precise size of pressure difference
- Increases with altitude
10
Q
Altimeter Mechanical Error
A
Caused by misalignment or slippage in gears
11
Q
Altimeter Density Error
A
- 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)
12
Q
Altimeter Hysteresis Error
A
A lag in indications due to elastic properties of the materials used to construct aneroids
13
Q
Altimeter Reversal Error
A
- Caused by rapid or abrupt attitude changes
- only momentary in duration
14
Q
Vertical Speed Indicator (VSI) Operation
A
- 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
15
Q
VSI Lag Error
A
- 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
16
Q
Calibrated Airspeed
A
Indicated airspeed corrected for instrument and position error
17
Q
Equivalent Airspeed
A
Calibrated Airspeed corrected for compressibility factor
18
Q
Airspeed Indicator Operation
A
- Measures difference between total pressure (pitot tube) and static pressure (static port) to get dynamic pressure
- Dynamic pressure is a direct indication of airspeed
19
Q
Airspeed Density Error
A
- 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
20
Q
Airspeed Instrument Error
A
Caused by mechanical errors present within the instrument
21
Q
Hysteresis Error
A
Lag in indications due to elastic properties of aneroids
22
Q
Airspeed Position Error
A
- Airframe disturbing airflow around pitot tube or static port
- Example is high angle of attack
- CAS corrects this
23
Q
Pitot Source Blocked
A
- Airspeed Indicator = increasing in climb / decreasing in descent
- Altimeter = unaffected
- VSI = unaffected
24
Q
One Static Source Blocked
A
All are inaccurate while slipping and very sensitive in turbulence
25
Both Static Sources Blocked
- Airspeed Indicator = decreasing in climb / increasing in descent
- Altimeter = Freezes
- VSI = Reads 0
26
Both Static and Pitot Sources Blocked
- Airspeed Indicator = Freezes
- Altimeter = Freezes
- VSI = Reads 0
27
Pitot Source Partially Blocked
- Airspeed Indicator =Reads 0
- Altimeter and VSI unaffected
28
Static Source Partially Blocked
- 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
29
Attitude Indicator Operation
- 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
30
Heading Indicator Operation
- 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
31
Mechanical Precession Heading Indicator Error
- Frictional forces cause gyro to precess
- Causes gyro instruments to drift 3º every 15 minutes
- Reset heading indicator every 15 minutes
32
Apparent Precession Heading Indicator Error
- 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
33
Turn and Slip Operation
- 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
34
Rate One Turn
- On L or R in turn and slip or turn coordinator
- 180º per minute
35
Turn Coordinator Operation
- 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
36
Magnetic Compass Operation
- 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
37
Variation
- Difference between magnetic north and true north
- Add westerly track / subtract easterly track to true track to get magnetic track
38
Acceleration Compass Errors
- Causes a turning error
- ANDS (Accelerate North Decelerate South)
- Error does not exist on north and south headings
39
Turning Compass Errors
- Causes an acceleration error
- SAND (South Advance North Delay)
- Error does not exist on east and west headings
