Preflight - Flight Instruments

Question 1

What instruments operate from the pitot/static system?

Answer 1

Altimeter
Vertical Speed Indicator
Airspeed Indicator

Question 2

How does an altimeter work?

Answer 2

Aneroid wafers expand and contract as pressure changes in turn changing the pointer of the instrument

Question 3

What type of errors are altimeter subject to?

Answer 3

Mechanical Errors: Differences between ambient temperature/pressure
Inherent Errors: Non standard temperature/pressure
-Warmer than standard: less dense air so true altitude is higher than indicated
-Colder than standard: more dense air so true altitude is lower than indicated
-Extreme cold: +10°C- -50°C pilots should add cold temperature correction
-High to low: True altitude is lower than indicated
-Low to high: True altitude is higher than indicated
*High to low/Hot to Cold look out below

Question 4

For IFR flight, what is the maximum allowable error for an altimeter?

Answer 4

More than 75 feet with correct pressure setting should be considered unreliable

Question 5

Define and state how to determine the following:
Indicated altitude
True altitude
Absolute altitude
Pressure altitude
Density altitude

Answer 5

Indicated: what is read from the altimeter with correct setting
True: Vertical distance of MSL
Absolute: Vertical distance of AGL
Pressure: Indicated by 29.92” setting, used to compute density altitude
Density: pressure altitude corrected for non standard conditons

Question 6

Does adjusting the altimeter’s Kollsman window setting have any effect on the altitude displayed to an ATC controller? Why?

Answer 6

No, encoding altimeter measured to 29.92”Hg on the transponder. The Kollsman window does not effect this information.

Question 7

How does the airspeed indicator operate?

Answer 7

Measures the difference in ram pressure from the pitot tube and atmospheric pressure from the static port.

Question 8

What are the limitations the airspeed indicator is subject to?

Answer 8

Must have proper air in the pitot and static system

Question 9

What are the errors that the airspeed is subject to?

Answer 9

Position error- caused by sensing of erroneous static readings
Density error- changes in altitude and temperature are not compensated for by the instrument
Compressibility error- packing air in the pitot tube at high speeds (resulting in higher indications) above 180 KIAS

Question 10

What are the different types of aircraft speeds?

Answer 10

Indicated: IAS shown on the instrument
Calibrated: CAS shows speed through the air, IAS corrected for instrument and position error
Equivalent: EAS, CAS corrected for compression in the air inside the pitot tube (CAS=EAS at STD pressure)
True: TAS, CAS corrected for non standard pressure/temperature (TAS=CAS as STD pressure)

Question 11

What airspeed are indicated by various color codes found on the dial of an airspeed indicator?

Answer 11

White arc: Flap operating
Lower White arc: Vso Stall speed in landing configuration
Upper White arc: Vfe maximum speed with flaps extended
Green arc: normal operating range
Lower green arc: Vs1 stall speed clean
Upper green arc: Vno maximum structural cruise
Yellow arc: Caution range
Red line: Vne never exceed speed

Question 12

How does the vertical speed indicator work?

Answer 12

VSI rate of pressure change instrument that gives a deviation from constant pressure. Uses an aneroid, static pressure and calibrated leak. Any change in static pressure cause the aneroid to compress or expand to move the needle.

Question 13

What are the limitations of a vertical speed indicator?

Answer 13

Not accurate until stabilized, sudden or abrupt movements lead to inaccurate indications.

Question 14

What instruments are affected when the pitot tube, ram, air inlet, and drain hole freeze?

Answer 14

Only airspeed affected, will behave similar to a altimeter

Question 15

What instruments are affected when the static port freezes?

Answer 15

Airspeed: Will be accurate at the altitude port became frozen, otherwise it will be inverse of altitude
Altimeter: Indicates altitude is became blocked
Vertical speed: Will indicate level flight

Question 16

If the air temperature is +6°C at an airport elevation of 1,200’ feet and a standard (average) temperature lapse rate exists, what will be the approximate freezing level?

Answer 16

4,200’

6°C / (average lapse rate 2°) = 3,000’ freezing level + 1,200’(field elevation)= 4,200’

Question 17

What corrective action is needed if the pitot tube freezes? If the static port freezes?

Answer 17

Pitot tube: use pitot heat

Static system: Use alternate static or break the instrument face

Question 18

What indications should you expect while using alternate air?

Answer 18

Altimeter: will indicated higher than normal altitude
Airspeed: will indicated greater airspeed
Vertical speed: Show a momentary climb

Question 19

What instruments contain gyroscopes?

Answer 19

Attitude
Heading Indicator
Turn coordinator/indicator

Question 20

Name several types of power sources commonly used to power the gyroscopic instruments in an aircraft?

Answer 20

Electrical
Pneumatic
Venturi tube
Wet/dry vacuum systems
Usually two different systems are used

Question 21

How does the vacuum system operate?

Answer 21

Vacuum or pressures systems use air to spin the gyroscopic systems
*vacuum is usually 4.5”-5.5” Hg

Question 22

What are two important characteristics of gyroscopes?

Answer 22

Rigidity: Gyro prevents the axis of rotation to tilt
-Attitude indicators
-Directional gyro
Precession: Force 90°from the direction of rotation.
-Turn coordinators

Question 23

How does the turn coordinator operate?

Answer 23

Uses precession of the gyro to estimate bank and rate of turn
Inclinometer measures the force of gravity and the force of inertia caused by the turn

Question 24

What information does the turn coordinator provide?

Answer 24

Miniature aircraft shows rate of turn, rate of roll, and direction of turn. Inclinometer shows quality of turn

 - Slip: ball inside the turn
 - Skid: ball outside the turn

Question 25

What is the source of power for the turn coordinator?

Answer 25

Driven by electricity or air

Question 26

How does a heading indicator work?

Answer 26

Uses rigidity in space, rotor turns on the vertical plane. The airplane moves around the gyro to indicate heading information.

Question 27

What are the limitations of a heading indicator?

Answer 27

≈55° bank
≈55° pitch
if limits are reach, instrument will tumble until caged

Question 28

What type of error is the heading indicator subject to?

Answer 28

Due to precession HI will drift from set heading typically 15° per hour

Question 29

How does the attitude indicator work?

Answer 29

Gyro mounted on the horizontal plane and used rigidity and space. Indicates the attitude relative to the true horizon

Question 30

What are the limitations of an attitude indicator?

Answer 30

Bank limits are usually 100° to 110°
Pitch limits are usually 60° to 70°
If limits are reached, it will tumble until restablized

Question 31

Is the attitude indicator subject to errors

Answer 31

Errors are uncommon
Can show nose high/low in acceleration/deceleration
Roll out of a 180° turn will show climb and opposite turn

Question 32

How does a magnetic compass work?

Answer 32

Magnets mounted on the compass card align themselves with line of magnetic forces

Question 33

What limitations does the magnetic compass have?

Answer 33

Jewel-and -pivot type mount allows for free movement up to 18° as steeper angles indications are unreliable

Question 34

What are the various compass errors?

Answer 34

Variation: angular difference between true and magnetic north
Deviation: Electrical and magnetic interference
Magnetic Dip: Accelerate North Decelerate South
Oscillation: Erratic movement caused by turbulence
Northerly errors: Undershoot North Overshoot South (≈to the latitude of the location)

Question 35

Describe the function of the following equipment acronyms: PFD, MFD, AHRS, ADC, FMS, FD, TAWS, TIS?

Answer 35

PFD: Primary flight display
MFD: Multi function display
AHRS: Attitude heading reference system 
ADC: Air data computer (sends information to PFD, AHRS, transponder)
FMS: Flight management system
FD: Flight director
TAWS: Terrain awareness and warning system
TIS: Traffic information service

Question 36

What is the function of a magnetometer?

Answer 36

Measures the strength of earth’s magnetic fields, provides information to AHRS for PFD

Question 37

Does an aircraft have to remain stationary during AHRS system initialization?

Answer 37

Some AHRS need to be initialized on the ground allowing proper attitude reference

Question 38

If a failure of one of the displays (PFD or MFD) occurs in an aircraft with an electronic flight display, what will happen to the remaining operative display?

Answer 38

In the event of failure, some systems offers reversion capability to display necessary information

Question 39

When a display failure occurs , what other system components will be affected?

Answer 39

Some systems, failure of a display will result in loss of nav, comms, and GPS

Question 40

What display information will be affected when an ADC failure occurs?

Answer 40

Inoperative airspeed, altitude, and VSI by red Xs indicate ADC failure

Question 41

What display information will be lost when an AHRS failure occurs?

Answer 41

An inoperative attitude by red X indicated AHRS failure

Question 42

How will loss of a magnetometer affect the AHRS operation?

Answer 42

Heading information will be lost