Category: Avionics Objective Questions

Avionics Multiple Choice Questions on “Orbital Mechanics and Clock Characteristics”.

1. Which of the following is the most fundamental for satellite navigation?
a) Power source in satellite
b) Position and acceleration of satellite
c) Distance from the Earth
d) Total number of satellites in the sky
Answer: b
Clarification: All of the satellite navigation equations have either satellite position or velocity as a variable. The linear independence of the equations, which dictate the observability of the navigation solution, is a function of the relative position of the satellites in orbit. Thus the position and the velocity of satellites is of primary importance.

2. What is the line connecting the intersection of the orbital plane with the Earth’s equatorial plane called?
a) Critical point
b) Intersection plane
c) Line of nodes
d) Differential line
Answer: c
Clarification: The line of nodes is the intersection of the orbital plane with the Earth’s equatorial plane. The ascending node and the descending node are the points where the satellite crosses the equatorial plane.

3. When the satellite crosses the equatorial plane from the southerly latitude to the northerly, the point is called descending node.
a) True
b) False
Answer: b
Clarification: The ascending node is the point where the satellite crosses the Earth’s equatorial plane from the southerly latitude to the northerly.

4. What is the number of independent constants required to specify the nominal orbit?
a) 6
b) 5
c) 2
d) 7
Answer: a
Clarification: Six independent constants are needed to specify the nominal orbit. These can be the three components of position and velocity at any instant of time and are used in the orbital mechanics equations.

5. The line connecting the perigee and apogee is called as?
a) Differential line
b) Line of apsides
c) Line of maximum reception
d) Overhead line
Answer: b
Clarification: The points where the satellite is closest and farthest from the Earth is called the perigee and apogee respectively. The line connecting the apogee and the perigee is called the line of apsides.

6. Which of the following is not one of the perturbations that make the satellite to vary from its elliptical path?
a) Solar activity
b) Asymmetrical components of Earth’s gravitational field
c) Air drag
d) Motion of a passing comet
Answer: d
Clarification: Perturbations cause the orbital plane to oscillate and rotate and vary the satellite from its elliptical orbital path. These forces include spherical asymmetrical components of Earth’s gravitational field, Lunisolar perturbations, air drag, magnetic and static electric forces.

7. The clocks are important in satellite navigation as they are potential sources of error.
a) True
b) False
Answer: a
Clarification: The navigational messages from a satellite include parameters describing the satellite’s clock offset and drift, which are predicted by the control segment. Any instability in the satellite’s clock causes this prediction to be in error, thus resulting in range and range rate errors in the user’s navigation solution.

8. Differential GPS corrects for satellite errors.
a) True
b) False
Answer: a
Clarification: Satellite clock errors, including those caused by SA dithering, are completely eliminated by DGPS, except for the SA dithering effects due to delays in estimating, broadcasting, and making the DGPS corrections.

Avionics Multiple Choice Questions on “Stellar Inertial Navigation Theory”.

1. Which of the following are false with respect to stellar navigation?
a) Can be used in daylight and at night
b) Position and altitude can be measured
c) Non-radiating
d) Cannot be jammed
Answer: b
Clarification: High precision stellar inertial navigation systems have been developed with automatic daylight and night star tracking system. These are highly useful for military aircraft in that they provide accurate position and attitude information, are autonomous, non radiation and are invulnerable to jamming.

2. Which of the following can be used to estimate the latitude in the northern hemisphere using the horizon as a reference?
a) North pole
b) Magnetic north
c) Polaris
d) Orion’s belt
Answer: c
Clarification: The north star or Polaris can be used to estimate latitude in the northern hemisphere using the horizon as a local level reference at the observers position. This type of navigation was used by the ancient mariners.

3. What is it called when the position is determined by angles between a star and an accurate time reference?
a) Position fix
b) Celestial fix
c) Sun fix
d) Horizontal fix
Answer: b
Clarification: Navigators on early transoceanic flights used sextants to manually measure star angle with respect to their local vertical. Using the line of sights form two or more stars, along with a star catalog and accurate time reference, the position in Earth latitude and longitude can be deduced. This was known as celestial fix.

4. Why is the inertial navigation system combined with celestial navigation system?
a) Correction of drift error
b) Deriving true north
c) Deriving magnetic north
d) Correction for weather effects
Answer: a
Clarification: Inertial navigational suffer from drift after long hours of using. Since the position error growth of these free inertial navigation systems was excessive on long flights, it was natural to periodically update their position with position updates from manual star fixing.

5. The sensors that maintain a centered star image for celestial navigation is called as _________
a) Star fixer
b) Celestial fixer
c) Star tracker
d) Star searcher
Answer: c
Clarification: The star sensors have a narrow field of view and maintain a centered star image through the gimbal drive commands and are called star trackers. They have day and night tracking capability, given reasonable cloud cover conditions.

6. Which of the following is required to integrate stellar navigation and inertial navigation to get the best estimate navigation solution?
a) Kalman filter
b) Star fix
c) Celestial fix
d) Multisensor processing
Answer: a
Clarification: Navigational systems use Kalman filtering techniques to integrate all the sensed navigational data to obtain the best estimate navigation solution. The use of Kalman filter to integrate stellar measurements requires that star observations and errors be correctly modeled.

7. The observability problems are greatly intensified if the telescope is rigidly mounted to the IMU.
a) True
b) False
Answer: a
Clarification: Observability problems associated with the Kalman filter are greatly intensified in a stellar inertial navigation system if the telescope is rigidly mounted to the IMU even though the IMU is gimballed to provide star pointing.

8. The inertial LOS to any star is precisely given from _______
a) Star tracker
b) Star catalog
c) Air data computer
d) Celestial fix
Answer: b
Clarification: The application of Kalman filter begins with the precise mathematical definition of the star observation. The inertial line of sight to any given star is precisely known from the star catalog.

9. The angular error is the angular difference between computed LOS and the physical star sensor LOS.
a) True
b) False
Answer: a
Clarification: The angular error which is measured by a star sensor is the angular difference between the computed (error corrected) LOS to the star and the physical star sensor LOS.

Avionics Interview Questions and Answers for freshers on “Flight Management Systems – 2”.

1. Both FMS 1 & 2 get information from only one FMC in the case of ______
a) Independent mode
b) Loss of one FMC
c) Single mode
d) Double mode
Answer: c
Clarification: In Single mode operating mode of the FMS two of the FMC is not in operation and this might cause one of the two FMS to fail. Hence both the FMS get information from one FMC.

2. The standby FMC performs calculations even when both the FMC are fully functional.
a) True
b) False
Answer: b
Clarification: The standby computer does not perform any calculations, but is regularly updated by the master FMC. In the case of a single FMC failure, the standby FMC provides data to FMS connected with the failed FMC.

3. What filter is used by the FMS to estimate the position of the aircraft from various sensors?
a) Kalman filter
b) Position error filter
c) GPS filter
d) Gyro and accelerometer filter
Answer: a
Clarification: The FMS combines the data from the navigational sources, comprising the inertial systems, GPS and the radio navigation systems, in a Kalman filter to derive the best estimate of the aircraft position. Each navigation system has its own advantages and limits, a Kalman filter combines the resource from all the systems to provide a more accurate position of the aircraft.

4. What is the output for the following system?

a) Aircraft position
b) All the fight data
c) Gyro and accelerometer values
d) Warning signals for wrong navigation
Answer: a
Clarification: The final output of a Kalman filter is the best estimated aircraft position derived from various radio and inertial/GPS sensors. The direct information from the sensors ( raw data) cannot be used directly for accurate position location as their error increases with time.

5. Which one of the following is not a navigation mode used by FMS for computing position of the aircraft?
a) Inertial (IRS) – GPS
b) Inertial (IRS) – DME/DME
c) Inertial (IRS) – VOR/DME
d) GPS only
Answer: d
Clarification: Each FMS computes the aircraft position and the position accuracy. The FMS computed position is an optimum combination of the inertial position and the GPS or radio position, depending on which equipment provides the most accurate data. This results in four navigation modes: Inertial (IRS) – GPS, Inertial (IRS) – DME/DME, Inertial (IRS) – VOR/DME, Inertial (IRS) only. The only GPS is not used as the position information is within a radius where the aircraft is flying.

6. Navigational functions are no longer available if the INS shuts down in an FMS.
a) True
b) False
Answer: a
Clarification: The FMS aircraft position always uses the inertial position. This computation is not possible if the inertial position is not valid, and in this case, all the FMS navigation and flight planning functions are no longer available. FBW system also fails in the case of an INS shut down since it uses INS for feedback.

7. What is the interval for updating data in the navigation database?
a) 1 hour
b) 1 month
c) 24 hours
d) 28 days
Answer: d
Clarification: The navigation database is updated every 28 days, according to the ICAO AiRAC cycle, and is held in non-volatile memory. It is clearly essential to maintain the recency and quality of the database and the operator is responsible for the detail contents of the database which is to ARINC 424 format.

8. Which one of the following is not a factor for calculating speed breaches by the FMS?
a) Aircraft weight
b) CG position
c) Wind and temperature models
d) Position of the aircraft
Answer: d
Clarification: The FMS continually monitors the aircraft envelope and ensures that the speed envelope restrictions are not breached. It also computes the optimum speeds for the various phases of the flight profile. This is carried out taking into account factors such as: Aircraft weight – computed from a knowledge of the take-off weight and the fuel consumed (measured by the engine flow meters), CG position – computed from known aircraft loading and fuel consumed, Flight level and flight plan constraints, Wind and temperature models, Company route cost index.

Avionics for Interviews,

Avionics Multiple Choice Questions on “Parallel and Serial Transmission”.

1. In a parallel communication, each bit requires a transmitter and receiver.
a) True
b) False
Answer: a
Clarification: In a parallel transmission each bit is transmitted in a separate wire. Since each bit is transmitted individually, each bit requires a separate transmitter and a receiver.

2. What is the cable that carries the information in parallel transmission called?
a) Parallel line
b) Data bus
c) Data line
d) Data link
Answer: b
Clarification: In a parallel transmission multiwire cables are used. These cables carry a bit in each wire and are referred as data bus.

3. Which of the following is a false reason for parallel lines not being used for long distances?
a) Cost factor
b) Signal Attenuation
c) Number of transmission channels
d) Low speed
Answer: d
Clarification: One of the major disadvantages of using parallel transmission for long distance is that laying the data bus is costly. To cover a distance of 10km for an 8 bit system, we need a cable of 80km length. Parallel data are usually faster than serial since all the bits are transmitted simultaneously.

4. Why higher speed communications in parallel transmission require shorter length?
a) Cost
b) Resistance
c) Inductive and capacitance effects
d) Noise
Answer: c
Clarification: As the speed of transmission or the frequency of transmission increases the wavelength of transmission becomes comparable with the length of the data bus. This causes inductive and capacitance effects which degrade the signal.

5. Which bit is transmitted first in a serial communication?
a) Least significant bit
b) Most significant
c) All the bits simultaneously
d) Not in any specific order
Answer: a
Clarification: In serial transmission, the bits are transmitted one after the other in a specific order. The least significant bit is transmitted first and the most significant bit is transmitted in the end.

6. In serial communication, if the time interval to transmit one bit is 10μs. What is the time to transmit an 8-bit word?
a) 8μs
b) 80μs
c) 0.8μs
d) 0.008μs
Answer: b
Clarification: Total transmission time = time for each bit x total number of bits = 8 x 10μs = 80μs.

7. In parallel communication, if the time interval to transmit one bit is 10μs. What is the time to transmit an 8-bit word?
a) 10μs
b) 100μs
c) 0.1μs
d) 0.01μs
Answer: a
Clarification: Since all the bits are transmitted simultaneously, the time taken for the transmission of one bit is equal to the time taken for the transmission of any number of bits. Therefore the time taken is 10μs.

8. The devices that convert serial to parallel and parallel to serial are called?
a) Serializer/Deserializer
b) Transmission converters
c) Multiplexer
d) Preemphasizer
Answer: a
Clarification: Parallel transmission is high speed and serial data can cover longer distances. Hence they are used interchangeably and the devices which convert serial to parallel and parallel to serial transmission is called serializer/deserializer device (SERDES).

Avionics Multiple Choice Questions on “Antenna Fundamentals”.

1. All EM waves propagate at the speed of light irrespective of medium.
a) True
b) False
Answer: b
Clarification: The speed of light depends on the medium through which it travels and it the same for EM waves as light can be thought of an EM wave. The speed of EM waves is maximum in a vacuum.

2. In a current carrying conductor, what happens to the magnetic field produced if the supplied voltage is increased and current is maintained constant?
a) Field strength increases
b) Field radius increases
c) Filed strength decreases
d) Does not change
Answer: d
Clarification: The magnetic field produced by a current carrying conductor is only influenced by the current and not the voltage. Since the current is maintained constant, there is no change in the magnetic field strength or radius.

3. Which of the following is the most necessary for an electric field to exist?
a) Current
b) Potential difference
c) Dielectric material
d) Metal conductor
Answer: b
Clarification: The most important thing for an electric field to exist is a potential difference between two conductors. It is not that only metal conductors can produce an electric field, potential difference between fluids also produces electric fields.

4. What happens to the electric field between two conductors when the permeability of the material between the plates is increased?
a) Field strength increases
b) Field radius decreases
c) Field strength decreases
d) Nothing happens
Answer: d
Clarification: The permeability of a material only affects the magnetic field and not the electric field. Electric field depends upon permittivity of the material between the two conductors.

5. Which of the following is not true?
a) A conductor carrying alternating current radiates
b) A transmission line must not radiate energy
c) Antennas are transmission lines which are made to radiate energy
d) A parallel wire transmission, when left open, does not radiate
Answer: d
Clarification: If a parallel-wire transmission line is left open, the electric and magnetic fields escape from the end of the line and radiate into space. This radiation, however, is inefficient and unsuitable for reliable transmission or reception.

6. The radiation from an open line can be increased by bending to which of the following angle?
a) 0°
b) 180°
c) 90°
d) 53.76°
Answer: c
Clarification: The radiation from a transmission line can be greatly improved by bending the transmission line conductors so that they are at a right angle to the transmission line. The magnetic fields no longer cancel and, in fact, aid one another. The electric field spreads out from conductor to conductor. The result is an antenna.

7. What is the ratio of the electric field strength of a radiated wave to the magnetic field strength called?
a) Impedance of space
b) Dielectric constant
c) Permittivity
d) Permeability
Answer: a
Clarification: The ratio of the electric field strength of a radiated wave to the magnetic field strength is a constant. It is called the impedance of space, or the wave impedance.

8. The fields in the Fresnel zone are radio waves that contain the information transmitted.
a) True
b) False
Answer: b
Clarification: The near field describes the region directly around the antenna where the electric and magnetic fields are distinct. These fields are not the radio wave, but they do indeed contain any information transmitted. The near field is also referred to as the Fresnel zone.

9. At what distance from the antenna does the far field start?
a) 2 wavelengths
b) 5 wavelengths
c) 10 wavelengths
d) 25 wavelengths
Answer: c
Clarification: The far field that is approximately 10 wavelengths from the antenna is the radio wave with the composite electric and magnetic fields. For example, at 2.4 GHz, one wavelength is 984/2400 = 0.41 feet. The far field is 10 times that, or 4.1 ft or beyond.

10. The Far field is also known as ______________
a) Fresnel zone
b) Fraunhofer zone
c) Maxwell zone
d) Marconi zone
Answer: b
Clarification: The far field is also called the Fraunhofer zone. It is named after the Bavarian physicist Joseph Ritter von Fraunhofer.

11. An Em wave is said to be vertically polarized when the angle between the electrical field and earth is _______
a) 50°
b) 20°
c) 90°
d) 180°
Answer: c
Clarification: Polarization refers to the orientation of magnetic and electric fields with respect to the earth. If an electric field is parallel to the earth, the electromagnetic wave is said to be horizontally polarized; if the electric field is perpendicular to the earth, the wave is vertically polarized.

12. Which of the following is not true?
a) Right circular polarized antennas can pick up left circular polarized waves due to propagation effects
b) Circular polarization has lesser attenuation in free space
c) Circular polarized wave can follow the curvature of earth
d) In circular polarization the electric and magnetic fields rotate as they leave the antenna
Answer: c
Clarification: In circular polarized wave the polarization angle of the electric field and the earth is continuously changing. This does not affect the transmission direction and hence circular polarized waves cannot bend with the curvature of earth, like any other EM wave.

13. What happens when a vertical or horizontal polarized antenna receives a circular polarized wave?
a) Gain increases
b) Signal strength increases
c) Signal strength reduces
d) Cannot receive circular polarized waves
Answer: c
Clarification: A vertical or horizontal antenna can receive circular polarized signals, but the signal strength is reduced. When circular polarization is used at both transmitter and receiver, both must use either left- or right-hand polarization if the signal is to be received.

14. Which of the following devices assist in using the same antenna for transmission and receiving?
a) Monoplexer
b) Multiplexer
c) Duplexer
d) Switch
Answer: c
Clarification: An antenna can transmit and receive at the same time as long as some means is provided for keeping the transmitter energy out of the front end of the receiver. A device called a duplexer is used for this purpose.

Avionics Multiple Choice Questions on “Atmospheric Effects on Satellite Signals”.

1. How does troposphere affect the satellite signals?
a) Reduces velocity
b) Reflects the signals
c) Refracts the signal
d) Bit inversion occurs
Answer: a
Clarification: The major sources of errors are when the signal pass through the atmosphere. The troposphere causes the propagation velocity of the signal to be slowed, compressing the signal wavelength.

2. Which of the following makes the existence of ionosphere possible?
a) Rotation of the Earth
b) Ultraviolet radiation from sun
c) Solar flares
d) Radiation from distant stars
Answer: b
Clarification: The ionosphere owes its existence to the ultraviolet radiation from the sun. The photons possess a certain amount of energy which is enough to break down electrons from their parent atom. The result is a large number of free, negatively charged, electrons and positively charged atoms and molecules called ions.

3. Satellite signals are refracted by the ionosphere.
a) True
b) False
Answer: b
Clarification: Below 30MHz frequency the ionosphere almost acts like a mirror reflecting the signal back to Earth. At higher frequencies, such as those used in satellite communication, radio waves pass through the atmosphere.

4. What happens to the satellite signals as the density of the ionosphere is high?
a) Velocity increases
b) Velocity decreases
c) Signal strength increases
d) Frequency reduces
Answer: a
Clarification: The velocity of the carrier, the pure sinusoidal wave, is increased in the presence of electrons. Thus the greater the density of electrons in the ionosphere greater the velocity of the signal.

5. What is the increase in velocity of the signal by the ionosphere termed as?
a) Differential velocity
b) Velocity advance
c) Phase advance
d) Signal advance
Answer: c
Clarification: The result of satellite signal travelling through ionosphere is that a particular phase of the signal arrives at the receiver earlier than it would have had if the signal travelled in a complete vacuum. This early arrival is termed as phase advance.

6. TEC in the ionosphere is a function of solar radiation.
a) True
b) False
Answer: a
Clarification: TEC or the total electron content in the ionosphere is a function of solar radiation. As more radiation falls on Earth, more number of molecules are ionized and hence TEC is more in the daytime than at the night.

7. Which of the following is true with respect to ionospheric scintillation effects?
a) It causes signal fading
b) Occurs at the equatorial and polar regions
c) Occurs mostly at day
d) Occurs when high solar activity is present
Answer: c
Clarification: Ionospheric scintillation causes signal fading and effects in the equatorial and the Polar Regions. Strong scintillation effects are rare localized at certain times during the night, and usually occurs during periods of high solar activity.

8. The refractivity of the troposphere is not a function of ________
a) Frequency
b) Temperature
c) Pressure
d) Partial pressure of water vapour
Answer: a
Clarification: Unlike the refractivity of the ionosphere, the refractivity of the troposphere is not the function of carrier frequency. At a given altitude it is determined from where P is total pressure, T is the absolute temperature, and e is the partial pressure of water vapour.