Category: Avionics Objective Questions

Avionics Multiple Choice Questions on “Modular Avionics Architectures & UAV Avionics”.

1. Which one of the following is not a true with respect to integrated modular avionics architecture?
a) Reduces weight
b) Easy maintenance
c) Hardware independent software
d) Increased life cycle
Answer: d
Clarification: An integrated modular avionics architecture system reduces weight as the processors are centralized and relatively fewer components are required. It is also easy for maintenance as each component is a separate block which can be repaired or replaced easily. Modular avionics architecture ensures that the software used is hardware independent and can be updated in the future. However they do not ensure increased life cycle of the components, the life cycle of a component is same if the architecture is modular or any other type.

2. The architecture where each component had its own sensors, processing and display is called as ________
a) Centralized architecture
b) Federated architecture
c) Disjoint or independent architecture
d) Open system architecture
Answer: c
Clarification: Disjoint architecture is a First generation architecture where the avionics systems were stand alone black boxes which had separate sensors, processors and displays and were linked together by point to point wiring.

3. Which one of the following is not true with respect with centralized architecture?
a) Complex design
b) Software can be written easily
c) Requires long data buses
d) Computers are in readily accessible bay
Answer: a
Clarification: The centralized architecture is one where all the components are linked to a single main frame computer for processing. The design is simple and software preparation and update is easy as the computer is easily accessible but requires long data buses running from the component to the computer which increases weight.

4. Which type of avionic architecture was the first to use DIAS?
a) Centralized architecture
b) Pave pillar architecture
c) Federated architecture
d) Open system architecture
Answer: c
Clarification: Federated avionic architecture is a type of second generation architecture in which the data from each avionic component was converted into digital information and sent to the main frame computer. This technology was called the DIAS or Digital Avionics Information System.

5. A time shared multiplex highway is used in Federated avionic architecture.
a) True
b) False
Answer: a
Clarification: The reason why time division multiplexing is possible is that the data transfer form the component to the computer is digital. This reduces a huge amount of wiring as the data transfer is serial and also the error is not propagated.

6. What advantage does the concept of IS2 add to the pave pace avionic architecture?
a) Cost reduction
b) Better performance
c) Easy maintenance
d) Software compatibility
Answer: a
Clarification: The total cost of sensors used in avionic systems costs around 70% of the total avionic system. IS2 is the concept of an integrated sensor system in which the sensors are shared by different avionic components thus reducing the overall cost.

7. Which avionic architecture allows the existence of heavily armed single seat fighters with a variety of weapons?
a) Federated architecture
b) Pave pillar architecture
c) Centralized architecture
d) Distributed architecture
Answer: b
Clarification: In a typical single seat fighter aircraft the pilot has to play the role of both controlling the aircraft and weapons management as opposed to a twin seat aircraft where the pilot flies the plane and the RIO or Radar Intercept Officer manages the weapons. Pave pillar architecture allows the pilot to be the weapons system manager without which single seat fighter aircraft like F-22 and the F-35 would not have been possible.

8. What type of avionic architecture is used in the JSF?
a) Pave pillar avionic architecture
b) Advanced integrated avionic architecture
c) Hierarchical avionic architecture
d) Centralized avionic architecture
Answer: b
Clarification: The Joint Strike Fighter’s sensors, communications, and flight-control systems will blend together more tightly than any other combat aircraft in history, and will revolve around high-speed fiber-optic data buses and powerful commercial off-the-shelf microprocessors using advanced integrated avionic architecture.

9. What is the cost-effective solution for UAV displays?
a) HMDs
b) HUDs
c) HDDs
d) No display for UAV
Answer: a
Clarification: Since the UAV is unmanned it does not require HDD or HUD but since the pilot is going to be on the ground controlling the UAV, HMDs are considered to be cost-effective and also show good performance and situational awareness.

10. What is the failure probability for a UAV?
a) 10/hour
b) 10²/hour
c) 10^-3/hour
d) 10^-5/hour
Answer: d
Clarification: Since the UAV is unmanned its failure would not be fatal, the failure probability for a UAV is less than that of a normal aircraft with a figure of 10^-5/hour. Although, a failure might cause damage to the UAV and where it falls. The failure probability differs from mission to mission.

11. Which one of the following is false with respect to TRN?
a) self contained
b) Unjammable
c) Low accuracy
d) No external systems needed
Answer: c
Clarification: Terrain reference navigation, TRN, systems are used in cruise missiles and aircraft. One of the major advantage in UAV/UCAV applications is that they are completely self-contained and unjammable as well as of high accuracy. They are completely independent of any external systems such as satellites or ground stations.

12. A flight management system is not necessary for simple UAVs.
a) True
b) False
Answer: a
Clarification: Although an FMS is needed for UAVs, for simple UAVs such as radio controlled models does not require FMS. The FMS functions of many smaller UAVs are carried in the ground station.

13. What is the altitude of HALE?
a) 20,000ft
b) 30,000ft
c) 40,000ft
d) 50,000ft
Answer: d
Clarification: HALE corresponds to High Altitude and Long Endurance aircraft. It has a service ceiling of 50,000ft and an endurance greater than 20hrs.

14. What type of communication does the MQ-9 ‘reaper’ UCAV use?
a) Satellite
b) Radio
c) Infrared
d) Microwave
Answer: a
Clarification: Since the MQ-9 has an endurance of 28hrs and range of 3,200nm it needs a communication system that is not affected by the curvature of the Earth. Satellite communication system is best suited for this as a minimum of 3 satellites is enough to have communication around the world using the technique of triangulation.

15. In a radio controlled UAV, FHSS technology has more advantage than DSSS technology.
a) True
b) False
Answer: b
Clarification: FHSS stands for frequency hopping spread spectrum and DSSS for Direct sequence spread spectrum. DSSS technology is more advantageous as it is less susceptible to noise and can not be easily jammed or hijacked.

Avionics Questions and Answers for Experienced people on “Data Conversion – 2”.

1. Sampling an analog signal produces pulse amplitude modulation.
a) True
b) False
Answer: a
Clarification: The modulator acts like a gating circuit that allows the analog wave for a particular time period producing a pulse. The amplitude of the pulse is the input to the ADC which converts the voltage into binary numbers.

2. What causes a new signal with frequency f_s-f_m to be created near the original signal?
a) Attenuation
b) Imaging
c) Aliasing
d) Distortion
Answer: c
Clarification: Aliasing occurs when a signal is sampled mistakenly at a frequency lesser than twice the input frequency. It causes a new signal with a frequency of f_s-f_m to be created near the original signal.

3. What type of filter is an antialiasing filter?
a) Band pass
b) High pass
c) Low pass
d) Band stop
Answer: c
Clarification: The antialiasing filter is basically just a low pass filter which allows signals with frequencies less than the cut off value to pass through. The cut off frequency is usually half of the sampling frequency.

4. Which of the following is not used in antialiasing filters?
a) Single stage RC or LC circuits
b) Multistage LC circuits
c) RC active filter
d) High order switched capacitor filter circuits
Answer: a
Clarification: An antialiasing filter must have good selective characteristics. The roll off rate of a single stage RC or LC circuit is too low and hence Multistage LC circuits, RC active filter and High order switched capacitor filter circuits are used.

5. What is sampling at a rate higher than the Nyquist frequency called?
a) Undersampling
b) Oversampling
c) Distortion
d) Aliasing
Answer: b
Clarification: Sampling at a rate twice the highest frequency is called as Nyquist frequency. When sampling is done at a higher rate than Nyquist frequency it is called as oversampling. Oversampling has both advantages and disadvantages.

6. Which of the following is not a disadvantage of oversampling?
a) High cost
b) More storage space
c) Less accuracy
d) High power consumption
Answer: c
Clarification: Accuracy of the conversion increases with an increase in sampling rate since discretization is reduced and we get a better digital replica of the original signal. As the frequency is high and the time period between samples are very low huge amounts of data are recorded and hence require high power and storage space eventually leading to high costs.

7. What is processing gain?
a) Gain added by the ADC
b) Improvement in SNR
c) Amplitude increment by ADC
d) Reduction in error by the ADC circuitry
Answer: b
Clarification: One of the major advantages of oversampling is that it increases the signal to noise ratio(SNR). It decreases the quantization noise by spreading it over a wider frequency. The increase in SNR is called the processing gain.

8. What is the process gain of a signal with bandwidth 20MHz and a sampling frequency of 100MHz?
a) 4dB
b) 5dB
c) 4.6dB
d) 125dB
Answer: a
Clarification: Processing gain(dB) = 10 log[ (f_s/2)/BW] = 10 log[ (100/2)/20]= 10 log[ (50/20)] = 4dB.

9. Which of the following is true with respect to undersampling?
a) High power
b) Greater than Nyquist frequency
c) Use low pass filters
d) Less memory size
Answer: c
Clarification: Undersampling causes aliasing which at the output of the ADC results in a wave with much lower frequency than the original signal. To reduce aliasing effects, antialiasing filters are used which acts as a low pass filter.

10. Which circuit is used to produce the IF for better selection and filtering?
a) Downconverter
b) Modulator
c) RC circuit
d) Gating circuit
Answer: a
Clarification: In radio receivers, a high-frequency signal is converted to a lower mixed frequency called an intermediate frequency (IF) where it can be more adequately filtered for improved frequency selection. A downconverter is a circuit that performs this equivalent of aliasing.

11. According to the sampling theorem, what is the minimum sampling frequency to retain all the information if the bandwidth of the signal is 20MHz?
a) 20MHz
b) 40MHz
c) 80MHz
d) 2MHz
Answer: b
Clarification: According to sampling theorem, minimum sampling frequency = 2 x 20MHz = 40MHz.

Avionics for Experienced people,

Avionics MCQs on “Types of Antenna – 2”.

1. What is the use of loading coil?
a) Correcting resonance to a desired frequency
b) Increasing the antenna gain
c) Sideband suppression
d) Increasing the range of the antenna
Answer: a
Clarification: When a vertical antenna is made less than one-quarter wavelength, the practical effect is a decreased inductance. The antenna no longer resonates at the desired operating frequency, but at a higher frequency. To compensate for this, a series inductor, called a loading coil, is connected in series with the antenna coil. The loading coil brings the antenna back into resonance at the desired frequency.

2. Why is top hat added to antennas?
a) To increase capacitance
b) Increasing the antenna gain
c) Sideband suppression
d) Increasing the range of the antenna
Answer: a
Clarification: A top hat is a structure that increases the capacitance to surrounding items, bringing the antenna back into resonance. Obviously, such an arrangement is too top-heavy and inconvenient for portable and mobile antennas. However, it is sometimes used in larger fixed antennas at lower frequencies.

3. In a parasitic array antenna, the conductors that are not connected to the transmission line is called as?
a) Driven element
b) Parasitic elements
c) Extra elements
d) Array elements
Answer: b
Clarification: A parasitic array consists of a basic antenna connected to a transmission line plus one or more additional conductors that are not connected to the transmission line. These extra conductors are referred to as parasitic elements, and the antenna itself is referred to as the driven element.

4. In a parasitic array the elements are shorted if they are connected to a conducting beam.
a) True
b) False
Answer: b
Clarification: The boom does not have to be an insulator. Because there is a voltage null at the center of a one-half wavelength conductor at the resonant frequency, there is no potential difference between the elements and so they can all be connected to a conducting boom with no undesirable effect. In other words, the elements are not “shorted together.”

5. Parasitic element that is typically about 5 percent longer than the half-wave dipole-driven element is called _______
a) Array element
b) Director element
c) Reflector element
d) Driven element
Answer: c
Clarification: The reflector, a parasitic element that is typically about 5 percent longer than the half-wave dipole-driven element, is spaced from the driven element by a distance of 0.15λ to 0.25λ. When the signal radiated from the dipole reaches the reflector, it induces a voltage into the reflector and the reflector produces some radiation of its own creating a highly focused beam in the direction of the driven element.

6. Why is the boom of the yagi antenna connected to a metal mast and electrical ground?
a) Better signal directivity
b) Increased bandwidth
c) Lightning protection
d) To avoid short circuiting
Answer: c
Clarification: The centers of the parasitic elements are neutral electrically; these elements can be connected directly to the boom. For the best lightning protection, the boom can then be connected to a metal mast and electrical ground.

7. Which of the following is not one of the types of driven array antenna?
a) Rectilinear antenna
b) Broadside antenna
c) End fire antenna
d) log periodic antenna
Answer:a
Clarification: Each element in a driven array antenna receives RF energy from the transmission line, and different arrangements of the elements produce different degrees of directivity and gain. The three basic types of driven arrays are the collinear, the broadside, and the end-i re. A fourth type is the wide-bandwidth log-periodic antenna.

8. What is the length of the shortest element in the yagi antenna?
a) One quarter the wavelength of the highest frequency
b) One quarter the wavelength of the lowest frequency
c) One half the wavelength of the highest frequency
d) One half the wavelength of the lowest frequency
Answer: c
Clarification: The lengths of the driven elements vary from long to short and are related logarithmically. The longest element has a length of one-half wavelength at the lowest frequency to be covered, and the shortest element is one-half wavelength at the higher frequency. The spacing is also variable.

To practice MCQs on all areas of Avionics,

Avionics Multiple Choice Questions on “Automatic Landing Systems”.

1. Auto land system is a must for _________ and above?
a) Category I
b) Category II
c) Category III
d) Category IV
Answer: b
Clarification: Air carrier aircraft that are authorized for precision approach below Category II must have an automatic landing system. Auto land systems use information from various landing systems like ILS Tacan and at some cases even GPS to safely land the aircraft.

2. The reduction of glide slope gain is called as________
a) Auto throttle
b) Auto gain
c) Auto attenuation
d) Gain scheduling
Answer: d
Clarification: During the final approach the glide slope gain in the auto land system is reduced in a programmed fashion and is called gain scheduling. Supplementary sensors must supply the vertical guidance below 100ft.

3. What is the nominal accuracy of radar altimeters below 100ft?
a) 5 ft
b) 10 ft
c) 20 ft
d) 1.5 ft
Answer: d
Clarification: Low range radar altimeters have a nominal accuracy of 1.5 ft below 100ft altitude and 2% of full scale at higher altitude. They have a low noise output that allows the derivation of vertical rate information.

4. Accurate calculation of aircraft height using the glide path deviations and distance information is not practical.
a) True
b) False
Answer: a
Clarification: The ILS cannot develop similar information as radar altimeter since the glide slope receiver provides from the zero DDM glide path which is not at a constant height across the width of the localizer course. Therefore, accurate calculation of aircraft height using the glide path deviations and distance information is not practical.

5. What is the wheel height where flare command is initiated?
a) 75ft
b) 100ft
c) 25ft
d) 5ft
Answer: a
Clarification: The flare command is initiated at a wheel height of about 75ft, well before the runway threshold. However, the radar altimeter may not be used prior to threshold due to uneven terrain or tidal variations.

6. __________ is the exponential path tangent to a horizontal plane several feet below the runway?
a) Flare
b) Ground roll
c) Taxi
d) Tide
Answer: a
Clarification: The flare is an exponential path tangent to a horizontal plane several feet below the runway, which ensures a positive touchdown.

7. What is done to reduce the error in localizer as the runway is approached?
a) Gain scheduling
b) Reduce speed
c) Increase angle of attack
d) Flare
Answer: a
Clarification: The localizer gain must be scheduled to decrease as the runway is approached because the surfaces of constant DDM coverage to make the error signal more sensitive to distant displacement.

8. British Trident and U.S. L-1011 aircraft was certified for category III A operations.
a) True
b) False
Answer: a
Clarification: In the early 1970s the British Trident and the U.S. L-1011 aircraft including their autoland systems were certified for Category III A operations in revenue service using guidance information form the ILS and other on-board sensors.

Avionics Multiple Choice Questions on “Helmet Mounted Displays”.

1. Which of the following is not true with respect to HMD (Helmet Mounted Display)?
a) The flight parameters are displayed in the visor of the helmet
b) HMD comprises of collimated display
c) Using HMD the pilot has a FOV (Field OF Vision) of 360° without moving his head
d) The flight parameters are displayed in the pilot’s line of sight
Answer: c
Clarification: The FOV of an HMD is 360° in the sense that the pilot can look around(by moving his head) in all direction and still view the flight parameters in his line of sight. If the pilot does not move his head the FOV the HMD provides ranges from35° to 50° depending upon the type of aircraft and its role.

2. Which one of the following is not an essential factor in integrating the HMD with the helmet?
a) Must not interfere with the oxygen mask
b) Protect eyes and head during high-speed ejection
c) Geometry of the cockpit
d) Overall minimum weight for comfort
Answer: c
Clarification: The geometry of the cockpit does not affect the HMD nor the helmet as the helmet is worn by the pilot and the FOV of the HMD moves with the pilot’s head. Some of the factors that are essential are the minimum weight for comfort while wearing the helmet for long flight hours and in high g maneuvers, crashworthiness of the helmet with HMD and communication systems integrated no interference with other objects in the cockpit such as oxygen mask as it is crucial at ejection at high speeds.

3. What is the weight the pilot will feel on his head while executing a 9g maneuver with an HMD helmet of weight 800g?
a) 7.2kg
b) 0.72kg
c) 70.06kg
d) 9kg
Answer: a
Clarification: 800grams = 0.8 kg, during a 9g turn the pilot will experience a gravitational force 9 times that of a normal person at Earth surface. The total weight felt by the pilot = 0.8 x 9 = 7.2kg. Typical HMD helmets weigh around 1kg and at 9g the weight felt by the pilot will be 9kg which is just acceptable.

4. Which does not affect the inertial forces felt by the pilot when accelerating or decelerating?
a) Positioning CG with the pivoting point of the head
b) Reduce the weight of the helmet
c) Keeping the head in the upright position
d) Reduce the moment of inertia about yaw and pitch axis
Answer: c
Clarification: Keeping the head always in an upright position is not an option for pilots since the pilot will lose situational awareness if he does so. The pilot will feel the inertial forces irrespective of his head position. By reducing the moment of inertia we can reduce the inertial torques experienced. Reducing weight and positioning the CG of the helmet with the pivoting point of head ensures that there are minimal out of balance moments.

5. What are the advantages of HMS (Helmet Mounted Sights) over HMD?
a) Display flight data in the pilot’s line of sight
b) Provide target locking capabilities by looking at the target
c) Provide a FOV of 360°
d) Provide enhanced vision by combining radar and FLIR
Answer: b
Clarification: A Helmet Mounted Sights in combination with a head tracker system provides effective means for the pilot to lock on to target. The pilot can look at the enemy aircraft and lock on to it. The relative position of the enemy is then calculated by the head position of the pilot and sent to missiles to engage the target. A typical seeker head needs to be pointed to within about 2° of the target to achieve an automatic lock on.

6. Monocular rivalry occurs due to the brain trying to concentrate on _________
a) two equal displays on both the eyes
b) two different displays on both the eyes
c) one eye with display and the other eye without display
d) both the outside world image and the displayed image in one eye
Answer: c
Clarification: Monocular rivalry occurs because the brain is trying to process different images from each eye and rivalry can occur between the eye with a display and the eye without a display. The effect is most significant when flying at night when one eye sees less light whereas the other eye sees more. To overcome this binocular system is used where both the eyes are presented with the flight parameters.

7. Why are IIT (Image Intensifier Tubes) used in HMD?
a) Clarity of outside world scene
b) Provide night vision capabilities
c) Terrain mapping
d) Compensation for parallax errors
Answer: b
Clarification: IIT is an image intensification device which complements the infrared viewing system by providing night vision. The image form the Image Intensifier Tube is a phosphor screen which emits green light in the centre of the visual band where the eye is most sensitive.

8. In what type of display is the image projected directly to the retina of the pilot?
a) Virtual reality display
b) Binocular HMD
c) God’s eye view display
d) Optical display
Answer: a
Clarification: Virtual reality displays are for future virtual cockpits where the image is directly projected onto the retina of the pilot by a raster scanned laser light beam. The current technology of implementing a virtual retinal display involves lasers, optical fibers and miniature vibrating mirrors for raster scanning the retina of the eye, together with coupling optics.

9. Which of the following does not provide a proper reason for not using HMD in civil aircraft?
a) No need of helmets in civil aircraft
b) Acoustic noise level in civil aircrafts is much lower
c) Situational awareness is needed in civil aircraft
d) An oxygen mask is required only in the case of cabin depressurization
Answer: c
Clarification: For a civil aircraft the situational awareness is not essential as they are inherently safer and do not execute high g maneuvers. Also, situational awareness is an important factor only when the flight parameters are rapidly changing, for a civil aircraft which is in steady level flight for most of its flight time situational awareness is not necessary.

10. HMD has less accuracy than HUD when it comes to the unguided weapon.
a) True
b) False
Answer: a
Clarification: Dealing with guided weapons system such as missiles and laser-guided bombs the accuracy of HMD is adequate enough but for unguided weapons such as guns, unguided bombs, and rockets the accuracy is not yet feasible since the HMD is constantly moving with the pilots head. Currently, the boresight angles for HMD are 8 to 10 mRad, whereas for HUD it is 1.5 to 2 mRad.