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Avionics - Air Data Systems, Altitude and Heading Reference Quiz(MCQ)
1 .
The different probes that disturb the airflow is called ______
A)
Intrusive probe
B)
Data probe
C)
Static probes
D)
Air data probe

Correct Answer :   Intrusive probe

Explanation : All of the sensing probes, except for the flush mounted static probe, are intrusive because they disturb the local flow over the body of the aircraft. Thus they are also called intrusive probes.

2 .
The absolute pressure of the still air surrounding the aircraft is called as______
A)
Absolute pressure
B)
Static pressure
C)
Constant pressure
D)
Stagnation pressure

Correct Answer :   Static pressure

Explanation : static pressure is the pressure of the still air surrounding the aircraft body even when the aircraft is moving. It is measured using static ports placed along the aircraft skin.

3 .
Where are self-aligning pitot tubes used?
A)
Bomber planes
B)
General aviation
C)
Commercial airliners
D)
High angle of attack fighter aircraft

Correct Answer :   High angle of attack fighter aircraft

Explanation : When the angle of attack and the sideslip angle are under 10°, they do not affect the pressure measurements much. In applications such as high angle of attack fighters, special self-aligning pitot tubes are used to measure the stagnation pressure.

4 .
Which of the following instruments use the pitot-static probe for its input?
A)
Altitude indicator
B)
Airspeed indicator
C)
Attitude indicator
D)
Vertical speed indicator

Correct Answer :   Attitude indicator

Explanation : The instruments that use pitot-static probe are airspeed indicator, altitude indicator or the altimeter and the vertical speed indicator. The attitude indicator uses the gyro to measure the orientation of the aircraft.

5 .
What is the difference between the static pressure and the stagnation pressure when the aircraft is stationary?
A)
Infinite
B)
No difference
C)
Static pressure
D)
Any random value

Correct Answer :   Static pressure

Explanation : when the aircraft is stationary, the pressure sensed by the static port is the free stream air pressure and the stagnation pressure ports are zero. Since the aircraft is not moving stagnation pressure is zero and hence the difference between the two values is the static pressure.

6 .
What are the tubes in the aircraft that carry the air pressure to the instruments is called as?
A)
Blue lines
B)
Pressure lines
C)
Pressure tubes
D)
Pneumatic plumbing

Correct Answer :   Pneumatic plumbing

Explanation : Pipes that carry the air pressure sensed from the pitot tube or the pitot-static tube to the air data computer and the various other flight instruments such as the airspeed indicator, altitude indicator and the vertical speed indicator is collectively referred to as pneumatic plumbing.

7 .
Which of the following is done to reduce the static defect?
A)
Deploy Flaps and slats
B)
Less weight as payload
C)
Streamlined configuration of the whole aircraft
D)
Wind tunnel tests to find spots of body-flow interference

Correct Answer :   Wind tunnel tests to find spots of body-flow interference

Explanation : Various wind tunnel tests are done to predict the optimum location for the static port so that the interference of the flow with the body is minimum. Since static defect is predictable, it can be corrected in the air-data computer.

8 .
What is the difference between the actual free stream pressure and the measured static pressure called?
A)
Static error
B)
Static defect
C)
Free stream error
D)
Dynamic pressure

Correct Answer :   Static defect

Explanation : The pressure that is sensed via the pitot-static port will be different from the actual free stream pressure due to the interference from the skin, angle of attack and the sideslip angle. This difference is referred to as the static defect.

9 .
What is the temperature of the air surrounding the aircraft called as?
A)
Static temperature
B)
Total temperature
C)
Overall temperature
D)
Stagnation temperature

Correct Answer :   Static temperature

Explanation : The outside air temperature is also called the static air temperature and is necessary for computing various parameters such as true airspeed, air density and for fire control aiming solutions.

10 .
What is the temperature measured by a probe on the exterior of a moving aircraft?
A)
Static temperature
B)
Constant temperature
C)
Stagnation temperature
D)
Free stream temperature

Correct Answer :   Stagnation temperature

Explanation : The temperature measured by the temperature probe on the exterior of a moving aircraft is called the stagnation temperature. It is always higher than the static temperature due to the heating effects of compressing air at higher speeds.

11 .
Why is a hole required at the rear end of the temperature probe?
A)
Reduce time lag
B)
Redundancy
C)
Convective cooling
D)
Dual measurements

Correct Answer :   Reduce time lag

Explanation : To avoid time lags in the temperature measurements, a leakage hole at the rear end of the probe allows for rapid exchange. For redundancy, multiple temperature probes are placed in different parts of the aircraft.

12 .
Which flight critical system is the angle of attack indicator a part of?
A)
Landing system
B)
Stall warning system
C)
Airspeed indicator system
D)
Rate of climb indicator system

Correct Answer :   Stall warning system

Explanation : When angle of attack sensors are installed on an aircraft they are usually apart of an independent stall warning or stall control system. Since such systems are flight critical, redundant sensors are usually installed.

13 .
The angle between the relative wind and the longitudinal datum line on the fuselage is called as?
A)
Glide angle
B)
Relative angle
C)
Flight path angle
D)
Angle of attack

Correct Answer :   Angle of attack

Explanation : Angle of attack is the angle, in the normally vertical plane of symmetry of the aircraft, at which the relative wind meets an arbitrary longitudinal datum line on the fuselage. Angle of attack, is important as it corresponds to the amount of lift produced and the dangerous condition of stall.

14 .
What error will a 10°C error in temperature shown in true airspeed?
A)
10 Knots
B)
20 Knots
C)
0.2 Knots
D)
Greater than 1 Knot

Correct Answer :   Greater than 1 Knot

Explaination : A 10°C error in the temperature will result in a true airspeed greater than 1 knot at a typical transport aircraft flight conditions.

15 .
The recovery factor for computing the static temperature does not account for _____
A)
Re-radiation
B)
Friction heating
C)
Isentropic compression
D)
Nonisentropic compression

Correct Answer :   Isentropic compression

Explanation : The recovery factor of the probe corrects the original measured temperature readings for frictional heating in the skin, re-radiation from the aircraft to the flow, and nonisentropic compression of air. It is given by η and is measured empirically.

16 .
Which is the optimum place for a temperature probe?
A)
Landing gear
B)
Exit of engine
C)
Inside cockpit
D)
Tip of vertical tail

Correct Answer :   Tip of vertical tail

Explanation : Probes may be mounted on the wing tips, vertical tail, forward fuselage or other areas where the local mach number is the same as the free stream mach number for all expected flight altitudes and speeds.

17 .
Which of the following is used to obtain the altitude from the static pressure?
A)
Standard atmospheric model
B)
Standard atmospheric tables
C)
International atmospheric data
D)
International atmospheric tables

Correct Answer :   Standard atmospheric model

Explanation : To determine the altitude from the measured static pressure, the standard atmospheric model has been established. The standard model gives the relation between a height and the properties of the atmosphere as the solution to a differential equation relating the difference in pressure.

18 .
What is the height called when the standard temperatures are used?
A)
Total altitude
B)
Pressure altitude
C)
Constant altitude
D)
Standard altitude

Correct Answer :   Pressure altitude

Explanation : The altitude at which the standard temperatures are used is called the pressure altitude. Pressure altitude is the altitude of the aircraft above sea level. It always takes it’s reference as sea level.

19 .
Which of the following altitude is measured by the pitot-static tube?
A)
Total altitude
B)
Pressure altitude
C)
Constant altitude
D)
Standard altitude

Correct Answer :   Pressure altitude

Explanation : Pressure altitude, as the name suggests, is the altitude derived from pressure measurements. It is measured from the static port of the pitot-static probe. The static pressure of air varies with altitude with approximately 101Kpa at sea level.

20 .
What is the speed of the aircraft relative to the ground called as?
A)
True airspeed
B)
Inertial speed
C)
Ground speed
D)
Relative speed

Correct Answer :   Ground speed

Explanation : When you stand on the ground with a radar speed gun pointing at the aircraft, the speed measured is called the ground speed and is measured relative to the ground. True airspeed is measured relative to the wind.

21 .
Where will the measurements of static pressure be most accurate?
A)
Trailing cone
B)
Tail of the aircraft
C)
Nose of the aircraft
D)
Wing tips of the aircraft

Correct Answer :   Trailing cone

Explanation : The most accurate value of static pressure is when the flow is least affected by the presence of the aircraft itself. In a trailing cone configuration, the probe is far behind the aircraft and is least affected by the flow.

22 .
Why is heating necessary in pitot-static tube?
A)
Increase the sensitivity
B)
Force the flow away from tube
C)
Ice formation
D)
Force the flow towards the flow

Correct Answer :   Ice formation

Explanation : Pitot-static tubes are generally placed with heating elements to stop the formation of ice in the orifice of the probe. Formation of ice on the probes causes erroneous readings and has lead to fatal air crashes.

23 .
Why are retractable pitot tubes used in stealth planes?
A)
Stealth configuration
B)
Aerodynamically efficient
C)
Use GPS for speed and altitude
D)
Error values in supersonic speeds

Correct Answer :   Stealth configuration

Explanation : Stealth planes, such as the B2 spirit stealth bomber, use retractable pitot tubes to maintain their stealth. When not in stealth mode they extend the probes for air data measurements.

24 .
Which are the factors that mach number does not depend on?
A)
Static pressure
B)
Static temperature
C)
Stagnation pressure
D)
Thrust produced by the aircraft

Correct Answer :   Thrust produced by the aircraft

Explanation : The mach number is computed from the corrected values of static and stagnation pressures. Mach number is comparatively easier to calculate than airspeed in supersonic speeds due to the compression shocks that form in the pitot tube.

25 .
What does the altitude rate essentially tell us?
A)
Rate of glide
B)
Rate of climb
C)
Rate of decent
D)
Vertical speed

Correct Answer :   Vertical speed

Explanation : Air data computers usually provide an output identified as altitude rate which is an outgrowth of the early pneumatic vertical speed indicators which suffer from undesirable lags. Altitude rate combines accelerometer readings and pneumatic readings.

26 .
Why is it dangerous to fly over hilly areas with pressure altitude?
A)
Costly
B)
Not the true altitude
C)
Not reliable
D)
Affected by temperature

Correct Answer :   Not the true altitude

Explanation : Pressure altitude is always referenced from the sea level. When flying over hilly areas, the actual altitude of the aircraft from the ground is definitely lesser than the pressure altitude, thus showing erroneous altitude readings.

27 .
______ is used for setting stabilizer position and high speed performance boundaries?
A)
True airspeed
B)
Altitude
C)
Mach number
D)
Calibrated airspeed

Correct Answer :   Mach number

Explanation : Mach number is used for programming stabilizer position for speed stability, defining high speed performance boundaries such as flutter onset, and for defining optimal cruise paths.

28 .
Which of the following does not come under air data computer?
A)
Pressure ports
B)
Computer
C)
Pressure transducers
D)
Output drivers for interfacing

Correct Answer :   Pressure ports

Explanation : A typical central air data computer is a box containing: the pressure transducers, associated excitation circuitry, and signal conditioning circuitry, the computer, and the output drivers that are compatible with interfacing subsystems.

29 .
Which one of the following is not a part of the processor subassembly?
A)
CPU
B)
Volatile RAM
C)
Non erasable ROM
D)
Non volatile RAM

Correct Answer :   Non erasable ROM

Explanation : The air data equations are solved in the processor assembly, which contains the CPU, memory for the operational flight program which can be electrically erased or EEPROM, data storage memory( usually a volatile RAM), and non volatile RAM.

30 .
Which of the following includes A/D conversions and packing of discrete signals into logical words?
A)
Signal processing
B)
Output processing
C)
Mainframe processor
D)
Input processing

Correct Answer :   Input processing

Explanation : Input processing usually involves A/D conversion and packing of discrete signals into logic words, plus implementation of special serial data interfaces.

31 .
Which one of the following is not an advantage of centralized architecture?
A)
Simple design
B)
Software is flexible
C)
Software is easily coded
D)
Computer is readily accessible

Correct Answer :   Software is flexible

Explanation :  In centralized architecture, the software is not flexible. A minor change or update in one of the parts of the software requires the whole software to be written and checked again. Updating the software to the rapidly changing hardware is not possible.

32 .
Which of the following is not an advantage of distributed air data system?
A)
Better accuracy
B)
Reliability
C)
Easy maintenance
D)
Elimination of pneumatic plumbing

Correct Answer :   Better accuracy

Explanation : Accuracy is independent of the architecture used. The accuracy of a CADC is same as that of a distributed air data system but might suffer from lags occurring from long lengths of tubing.

33 .
Which system has replaced the CADC by using smaller and cheaper microprocessors?
A)
FADEC
B)
Inertial system
C)
Navigational system
D)
Distributed air data system

Correct Answer :   Distributed air data system

Explanation : With the advent of smaller and cheaper microprocessors, it became possible to pack them with probes and transducers. The result is a distributed air data system that replaces the CADC. A key feature is the packing of signal processing units with or adjacent to the probes.

34 .
Which of the following cannot be used to obtain an approximate velocity?
A)
Primary radar
B)
GPS
C)
Doppler radar system
D)
Inertial navigation system

Correct Answer :   Primary radar

Explanation : Velocity from Doppler, inertial and GPS can be used as an approximation for velocity. It is possible for the radio controller on the ground to obtain the velocity of the rotorcraft but it is not possible for the pilot to get velocity data from primary radar.

35 .
The conventional pitot tube cannot be used under______
A)
2 knots
B)
40 knots
C)
80 knots
D)
100 knots

Correct Answer :   40 knots

Explanation : The conventional pitot tube and the pressure transducer become ineffective as airspeed drops below 40 knots. At the lower speeds, impact pressure is equal to dynamic pressure q, and the sensitivity of this pressure to a change in velocity is minimal.

36 .
The configuration in which multiple pressure ports are located in the aircraft forebody is called as _____
A)
Multiple port system
B)
Nose cone port system
C)
Flush air data system
D)
Redundant air data system

Correct Answer :   Flush air data system

Explanation : Hypersonic vehicles used the concept of locating multiple pressure ports around an aircraft forebody to extract total pressure and flow direction. This type of configuration is referred to as the flush air data system and has been used at NASA Dryden research flights.

37 .
What is the approximate accuracy of laser velocimeter?
A)
10 knots
B)
2.5 knots
C)
1 knot and below
D)
0.14 knots

Correct Answer :   1 knot and below

Explanation : Test results show an accuracy of 1 knot or better at altitudes where the particle density is adequate. Aerosol densities and particle densities vary with altitude, time and volcanic eruptions.

38 .
What instrument measures the velocity by Doppler shift from backscatter of aerosol particles?
A)
Doppler radar
B)
Laser pitot tube
C)
Rotating anemometer
D)
Laser velocimeter

Correct Answer :   Laser velocimeter

Explanation : In a laser velocitimeter, optical sensors are located within the aircraft and look out through the flow into the free stream. They measure the Doppler shift from backscatter of naturally occurring aerosol particles in the free stream.

39 .
What is required to accommodate for the ground effect in swiveling pitot tube below rotor system?
A)
Radio altimeter
B)
GPS
C)
Doppler
D)
Secondary radar

Correct Answer :   Radio altimeter

Explanation : The principle of the probe is that the horizontal component of the induced flow velocity is a repeatable function of horizontal airspeed but varies with ground proximity. Hence, a radar altimeter is required to accommodate the ground effect.

40 .
Why is the static source errors compensated in helicopters?
A)
Not economical
B)
Due to difference in rotor down wash
C)
Requires high computational power
D)
Static source error does not matter

Correct Answer :   Due to difference in rotor down wash

Explanation : Static-source errors in helicopters tend to be difficult to compensate because of rotor downwash that differs significantly in and out of ground effect. Fixed wing aircraft do not compensate for static source errors in ground effect, and neither do helicopters.

41 .
Device that causes the magnitude of pressure to change when the aircraft speed nears zero are called ______
A)
Stall indicators
B)
Airspeed indicator
C)
Low speed indicators
D)
Rotating anemometer

Correct Answer :   Rotating anemometer

Explanation : Rotating anemometer increases the magnitude of pressure change caused by the change in airspeed when the aircraft airspeed is near zero. They are used in low omni range airspeed systems for helicopters.

42 .
Which of the following is false with respect to rotating anemometer?
A)
High sensitivity
B)
Used in low speeds
C)
Airspeed is measured in forward direction
D)
Can be used within the rotor blade

Correct Answer :   Airspeed is measured in forward direction

Explanation : Rotating anemometer is like a pitot tube for helicopters to measure low velocities below 40 knots. In addition to obtaining improved sensitivity at low speeds, the rotating probe measures omnidirectional airspeed, including backward velocities.

43 .
Airspeed measurements can be made by measuring the vortex’s _______
A)
Vorticity
B)
Strength
C)
Frequency
D)
Direction

Correct Answer :   Frequency

Explanation : A vortex sensor measures vortices shed by fluid flow over a deliberately-inserted obstruction. The frequency of vortices is proportional to the airspeed. This method has been used in helicopters and in ground vehicle fire control systems.

44 .
Which of the following systems use a gimballed pitot tube?
A)
Rotating pitot tube
B)
Rotating anemometer
C)
Omni directional pitot tube
D)
Swiveling pitot tube below rotor

Correct Answer :   Swiveling pitot tube below rotor

Explanation : In the swiveling pitot tube below rotor system, a gimballed pitot tube containing vane arrangement that causes the tube to align with the airflow within the downwash field emanating from the rotor blades is used. Changes in the airflow field vector are correlated with changes in true airspeed.

45 .
How to determine the true vertical reference?
A)
Time average of apparent vertical
B)
Integration
C)
Differentiating
D)
Sum of all the apparent vertical

Correct Answer :   Time average of apparent vertical

Explanation : The simplest approach to the determination of the true vertical is to time-average the direction of the apparent vertical(vector sum of gravity and vehicle acceleration).

46 .
When is the gyro interrupted in erection cutoff method?
A)
Deviation is low
B)
Deviation is large
C)
Never interrupted
D)
Always interrupted

Correct Answer :   Deviation is large

Explanation : The error caused in the vertical referencing can be rectified by introducing nonlinearities. One such method is the erection cutoff where the precession of the gyroscope is interrupted when a large deflection is sensed.

47 .
Which one of the following is the basic vertical reference in all forms of heading and attitude devices?
A)
Earth’s magnetic field
B)
Earth’s gravitational field
C)
Line perpendicular to actual horizon
D)
Line perpendicular to artificial horizon

Correct Answer :   Earth’s gravitational field

Explanation : The basic vertical reference in all forms of heading and attitude reference devices is the Earth’s gravitational field. The direction of Earth’s gravitational field can be sensed with great accuracy in stationary systems. However, when the platform moves, all the instruments indicate the vector sum vehicle acceleration and local gravity.

48 .
Which of the following is used to sense aircraft magnetic fields?
A)
Gyroscope
B)
Accelerometer
C)
Magnetic compass
D)
Airborne magnetometer

Correct Answer :   Airborne magnetometer

Explanation : Aircraft have magnetic fields that add to the Earth’s field and are sensed by the airborne magnetometers. The induced error, called deviation, can be 10° or more.

49 .
Why does magvar have diurnal change?
A)
Static buildup error
B)
Sensitivity of the instruments
C)
Magnetic pole migration
D)
Variation in aircraft magnetic effects

Correct Answer :   Magnetic pole migration

Explanation : Magvar has a diurnal change, a long term change due to the migration of magnetic poles, and random changes because of magnetic storms. The magnitude of the magnetic field changes about 0.5% per year.

50 .
Which of the following is not the angle between the horizontal component of B and true north?
A)
Magvar
B)
Dip angle
C)
Magnetic variation
D)
Magnetic declination

Correct Answer :   Dip angle

Explanation : The magnetic declination, also called the magnetic variation or magvar, is the angle between the horizontal component of B and true north. Navigators use ‘magvar’ in order not to confuse astronomical declination with magnetic declination.

51 .
Which of the following is not a unit of the magnetic field?
A)
Maxwell
B)
Tesla
C)
Gauss
D)
Gamma

Correct Answer :   Maxwell

Explanation : The magnetic fields B are measured in Gauss and Tesla(104 Gauss). In geomagnetism, Units of “Gamma”(10-5 )are used.

52 .
What can be done to reduce to avoid poor acceleration error averaging?
A)
Use higher order leveling loop
B)
Use switch gravity sensors
C)
Use differential leveling loop
D)
Use lowest order leveling loop

Correct Answer :   Use higher order leveling loop

Explanation : The stand off error depends upon the gravity sensors switch’s dead and gives poor acceleration errors. Significant improvement can be obtained in the averaging vertical reference by using a high order leveling loop.

53 .
The error that occurs due to the rotation of Earth as well as the aircraft’s own motion is called as ______
A)
Asymmetrical error
B)
Precession rate error
C)
Rate compensation error
D)
Standoff constant error

Correct Answer :   Standoff constant error

Explanation : A stand off constant error exists since the direction of the local vertical changes as a result of both the rotation of the Earth and the aircraft’s own motion around the Earth.