Category: Avionics Objective Questions

Avionics Question Bank on “Instrument Landing Systems – 2”.

1. What is the type of receiver used for marker beacon?
a) Heterodyne
b) Super Heterodyne
c) Capacitative pick off
d) Crystal controlled
Answer: d
Clarification: The marker beacon receiver is a dedicated crystal controlled receiver fixed tuned to 75 MHz. This is because all marker beacons use the same frequency.

2. Which of the following cause multi path signals?
a) Low transmission power
b) Ground reflection
c) Low frequency transmission
d) High frequency transmission
Answer:b
Clarification: Mulit path Signals are created when a part of the original signal take a different path than LOS to reach the receiver. Thus a signal with same information reaches the receiver at multiple times. Multi path signals are created when the actual signal gets reflected from the ground and reaches the receiver.

3. Which of the following transmits an audio Morse code?
a) Localizer
b) Glide slope transmitter
c) DME
d) Marker beacons
Answer: a
Clarification: An audible Morse code identification signal is transmitted on the localizer frequency. A voice channel from the control tower may also be provided.

4. ______________ provides deviation when the aircraft is displaced laterally from the vertical plane of the runway?
a) Localizer
b) Glide slope transmitter
c) DME
d) Marker beacons
Answer: a
Clarification: The localizer establishes a radiation pattern in space the provides a deviation signal in the aircraft when the aircraft is displaced laterally from the vertical plane containing the runway center line.

5. What is the signal that are added to the localizer signal, if the beam is narrow, to provide signal coverage?
a) Localizer plus
b) Difference signal
c) Sum signal
d) Clearance signal
Answer: d
Clarification: When the localizer CSB pattern is narrow, to reduce reflections from buildings and other aircraft, the system requires the addition of “clearance” signals to provide 35° coverage in both directions.

6. What type of antenna is used in the localizer?
a) Long periodic antenna
b) Helical antenna
c) Dipole antenna
d) Parabolic antenna
Answer: a
Clarification: Almost all of the localizer antenna is long periodic antenna. It provides unidirectional radiation, can be installed without guy cables and has good broadband characteristics.

7. Clearance signals can be transmitted from the same array antenna as the localizer signal.
a) True
b) False
Answer: b
Clarification: Clearance Signals, when required, can be provided by a separate array antenna specifically for clearance signals. In some designs, both clearance signals and localizer signals are transmitted from different elements of the same array. Nevertheless, the same antenna cannot be used.

8. What is the type of glide slope that depends on the reflection of signals by the ground?
a) Reflection slope
b) Refraction glide slope
c) Image glide slope
d) Direct glide slope
Answer: c
Clarification: Image array glide slope systems depend on reflections from the ground in the direction of approaching aircraft to form the radiation pattern.

9. What is the radiation pattern of the marker beacons?
a) Triangle
b) Circle
c) Square
d) Fan shape
Answer: d
Clarification: Marker beacons provide pilot alerts along the approach path. Each beacon radiates a fan shaped vertical beam that is approximately ±40° wide along the glide path by ±85° wide perpendicular to the path.

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Avionics Multiple Choice Questions on “Control and Data Entry”.

1. What type of beams are used for the tactical control panel?
a) Matrix array of infrared beams
b) Light beams
c) Lasers
d) Microwave beams
Answer: a
Clarification: A typical tactical control panel uses a matrix of infrared beams across the surface of the display containing various functional keys. Touching a specific function key on the display surface interrupts the x and y infrared beams which intersect over the displayed key function and hence signal the operation of that particular key function.

2. What is DVI control?
a) Direct voice input
b) Digitally vectored input
c) Digital voice input
d) Direct vectored input
Answer: a
Clarification: DVI control is direct voice input control through which the pilot can enter flight and navigational commands through voice.

3. In a DVI control, which system recognizes the pilot’s control?
a) Flight data computer
b) Air Data Computer
c) Speech recognition system
d) Central command center
Answer: c
Clarification: The commands given by the pilot is recognized by a speech recognition system which compares the spoken audio with preloaded vocabulary templates. If the command is recognized indication is given either aurally or visually to confirm the command.

4. The main reason for DVI control system in aircraft is _____________
a) less weight
b) latest technology
c) reduce pilot work load
d) space constraints
Answer: c
Clarification: DVI control system is used to control the aircraft using voice commands, thus the pilot need not have to operate push buttons, switches. This reduces the workload on the pilot during heavy workload operations such as combat.

5. What are isolated word recognizers?
a) Systems that can recognize anyone’s voice
b) System that is not fully voice commanded
c) Systems that require a pause between each word to recognize
d) Systems that only accept one-word command
Answer: c
Clarification: An isolated word recognizer requires pauses between each word said as it cannot recognize fully connected speech. The DVI control in an aircraft must not be an isolated voice recognizer to ensure smooth man-machine interface.

6. The DVI control system need not be super sensitive to the voice of the pilot.
a) True
b) False
Answer: b
Clarification: The DVI control system must be super sensitive to the voice of the pilot so that it can be operated in cockpit noise environment. In a fast jet combat aircraft, the background noise levels can be very high.

7. What is the reason for using speech synthesizers in aircrafts?
a) Communication with ATC
b) Communication with another aircraft
c) Used in flight data recorder
d) Warning messages to pilot
Answer: d
Clarification: Speech synthesizers are used to provide voiced warning messages to the pilot of system malfunctions and failures. They also aid DVI systems to provide feedback that a spoken command has been correctly recognized.

8. The audio/tactile management system combined with FBW and automated engine control is called ________
a) autopilot
b) flight management system
c) voice, throttle, stick control
d) flight control computer
Answer: c
Clarification: When the audio/tactile system, FBW, and the automated engine control is combined it is called the Voice, Throttle, Stick control. It is used in fighter aircraft such as Eurofighter Typhoon to reduce pilot workload.

9. What is the role of eye trackers in cockpits?
a) Improve concentration
b) Improve accuracy for targeting
c) Monitor pilot health
d) Assist in high g maneuvers
Answer: b
Clarification: Using an eye tracker the pilot’s gaze can be measured with accuracy which helps in better targeting. A fast and accurate data system can be achieved by this means without any discomfort to the pilot. They can track the eye by exploiting the principle of corneal reflection.

10. Why is the stereo sound warning system used?
a) Better sound clarity
b) Warning sound from the actual direction of a threat
c) To cancel the heavy background noise
d) To hear sound external to the aircraft
Answer: b
Clarification: A stereo sound warning system is used to produce a warning signal with the direction of threat. It consists of speakers mounted all around the cockpit, if the threat is approaching from the left side, the speakers on the left side produce signals to warn the pilot.

11. Only the pilot of a particular aircraft can use its DVI control system?
a) True
b) False
Answer: b
Clarification: The DVI control system is a universal system which can recognize the voice of anyone if spoken clearly. This is done for maintenance purposes and for an emergency.

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Avionics Multiple Choice Questions on “Digital Signal Processing”.

1. Any digital computer can be used for DSP.
a) True
b) False
Answer: a
Clarification: DSP is the use of a fast digital computer or digital circuitry to perform processing on digital signals. Any digital computer with sufficient speed and memory can be used for DSP.

2. What happens after the signal is passed through the analog to digital converter in a DSP?
a) Changed back to analog
b) Stored in a RAM
c) Amplified
d) Attenuated
Answer: b
Clarification: When the signal is converted from analog to digital it is a sequence of binary numbers which is stored in the RAM. A user defined code that is usually stored in the ROM performs mathematical and other manipulations after which it is converted back into analog signals.

3. Who is credited with creating the stored program concept?
a) John Von Neumann
b) Larry Page
c) Alan Turing
d) Ken Thompson
Answer: a
Clarification: Physicist John Von Neumann is generally credited with creating the stored program concept that is the basis of operation of all digital computers. Binary words representing computer instructions are stored sequentially in a memory to form a program. The instructions are fetched and executed one at a time at high speed.

4. What is the accessibility limitation of only one data or instruction set at a time from the memory called?
a) Von Neumann limitation
b) Von Neumann limit
c) Von Neumann speed
d) Von Neumann bottleneck
Answer: d
Clarification: The accessibility limitation of only one data or instruction set at a time from the memory is called as Von Neumann bottleneck. This has the effect of greatly limiting the execution speed.

5. Which type of architecture uses different storage space for program code and the data?
a) Von Neumann architecture
b) Harvard architecture
c) Fragmented architecture
d) Split cell architecture
Answer: b
Clarification: In a Harvard architecture microprocessor, there are two memories, a program or instruction memory, usually a ROM, and a data memory, which is a RAM. Also, there are two data paths into and out of the CPU between the memories. Because both instructions and data can be accessed simultaneously, very high-speed operation is possible.

6. What is the reason for the need of high speed DSP?
a) Less power consumption at higher speeds
b) Better processing capabilities
c) High sampling frequency
d) Easily programmable
Answer: c
Clarification: The time taken for input/output and the processing time together must be smaller than the sampling period to ensure the continuous flow of data. Since high sampling frequencies are needed for accurately converting the analog signal to digital, high speed DSP is a must.

7. Selectivity in a DSP is better than its analog equivalent.
a) True
b) False
Answer: a
Clarification: With DSP, the filters can have characteristics far superior to those of equivalent analog filters. Selectivity can be better because of the ease of controlling binary numbers, and the passband or reject band can be customized to the application.

8. Reduction in the number of binary words required to represent an analog signal is called ________
a) Undersampling
b) Oversampling
c) Data compression
d) Data minimization
Answer: c
Clarification: Data compression is a process that reduces the number of binary words needed to represent a given analog signal. Since analog to digital conversion produces a huge amount of data, for transmission it is a necessity that data is compressed.

9. What is the process of examining the frequency content of a signal?
a) Signal decoding
b) Spectrum analysis
c) Signal analysis
d) Data analysis
Answer: b
Clarification: Spectrum analysis is the process of examining a signal to determine its frequency content. Algorithms such as discrete Fourier transform (DFT) and FPGA is used to analyze the frequency content of an input signal.

10. What is the program that is used to speed the spectrum analysis process?
a) DDFT
b) FDFT
c) FGPA
d) Fast Fourier transforms
Answer: d
Clarification: The DFT is a complex program that is long and time-consuming to run. In general, computers are not fast enough to perform DFT in real time as the signal occurs. Therefore, a special version of the algorithm has been developed to speed up the calculation. Known as the fast Fourier transform (FFT), it permits real-time signal spectrum analysis.

11. Which of the following is not possible when the signal is analog?
a) Phase shifting
b) Equalization
c) Modulation
d) Data compression
Answer: d
Clarification: Data compression is done by checking redundancy in data. Data redundancy checking is only possible when the data is in digital form and hence data compression cannot be done in analog signals.

Avionics Multiple Choice Questions on “Satellite Subsystems”.

1. Which of the following is not a satellite subsystem?
a) Ground station
b) Power system
c) Telemetry tracking
d) Communication subsystem
Answer: a
Clarification: The communication subsystem is the most important part of the satellite. It requires varies additional systems like the power system, propulsion system, telemetry system for its proper functioning. The ground system however is not one of the satellite subsystem and is independent of the satellite. It is just a transponder to monitor and command the satellite.

2. Which of the following is not a part of the propulsion subsystem of a satellite?
a) Gyroscope
b) Jet thruster
c) AKM
d) Fuel control system
Answer: a
Clarification: The propulsion subsystem consists of the AKM(Apogee kick motor), jet thruster and the fuel control system. Gyroscopes and other attitude systems fall under the attitude control subsystem.

3. Which of the following are common baseband signals transmitted from the earth ground station?
a) Navigational data, computer data, video
b) Computer data, navigational data, voice
c) Voice, video, computer data
d) Computer data
Answer: c
Clarification: An earth station takes the signals to be transmitted, known as baseband signals, and modulates a microwave carrier. The three most common baseband signals are voice, video, and computer data.

4. Which of the following components receives, translates the signal frequency and re-transmits the signal in a satellite?
a) Repeater
b) Relay
c) Transponder
d) Transducer
Answer: c
Clarification: The uplink signals from earth are amplified, translated in frequency, and re-transmitted on the downlink to one or more earth stations. The component that performs this function is known as a transponder.

5. Why is there a huge spectrum space between the transmitted and received signal in satellite communication?
a) Reduce interference
b) Maximum efficiency
c) Less attenuation
d) To reduce space occupied by filters
Answer: a
Clarification: Because of the close proximity of the transmitter and the receiver in the satellite, the high transmitter output power for the downlink is picked up by that satellite receiver. Naturally, the uplink signal is totally obliterated. Furthermore, the transmitter output fed back into the receiver input causes oscillation. To avoid this problem, the receiver and transmitter in the satellite transponder are designed to operate at separate frequencies. In this way, they will not interfere with each other.

6. Which of the following transponders convert the uplink signal to downlink signal using two mixers
a) Single conversion transponders
b) Dual conversion transponders
c) Regenerative transponders
d) Dual mixer transponder
Answer: b
Clarification: A dual-conversion transponder makes the frequency translation in two steps with two mixers. No demodulation occurs.

7. In a regenerative transponder, the signal is demodulated and modulated again before transmission.
a) True
b) False
Answer: a
Clarification: A regenerative repeater demodulates the uplink signal after the frequency is translated to some lower intermediate frequency. The recovered baseband signal is then used to modulate the downlink signal.

8. What is the number of transponders if the satellite uses 12 channels of frequency and frequency reuse is implemented?
a) 12
b) 6
c) 24
d) 3
Answer: c
Clarification: Since in frequency reuse each channel can be used twice the numbers of transponders are also doubled. 12 x 2 = 24 transponders, two for each frequency.

9. Why is it not possible to provide transmit function by wideband amplifier and mixer circuits?
a) Heavy attenuation
b) High power output over wideband is not possible
c) Economically not profitable
d) Weight of the system increases five fold
Answer: b
Clarification: it is generally not possible to generate very high output power over such wide bandwidth. The fact is that no components and circuits can do this well. The high-power amplifiers in most transponders are traveling-wave tubes that inherently have limited bandwidth. They operate well over a small range but cannot deal with the entire 500-MHz bandwidth allocated to a satellite.

10. Which of the following is not true?
a) Battery is only used as a back up
b) When in orbit, solar power is always available
c) Battery is used for initial satellite orientation and stabilization
d) The batteries are charged using solar power
Answer: b
Clarification: When a satellite goes into an eclipse or when the solar panels are not properly positioned, there is a temporary cut in solar power supply. In situations like this the batteries take over temporarily and keep the satellite operating. The batteries are not large enough to power the satellite for a long time; they are used as a backup system for eclipses, initial satellite orientation and stabilization, or emergency conditions.

11. Telemetry, command, and control (TC&C) subsystem allow a ground station to monitor and control conditions in the satellite.
a) True
b) False
Answer: a
Clarification: The telemetry system is used to report the status of the onboard subsystems to the ground station. The telemetry system typically consists of various electronic sensors whose data are selected by a multiplexer and then converted to a digital signal, which then modulates an internal transmitter. This transmitter sends the telemetry information back to the earth station, where it is recorded and monitored.

Avionics online test on “Gyroscopes – 2”.

1. Which of the following systems do not use MEMS gyro?
a) Space launch vehicles
b) Flight control systems
c) Missile guidance
d) Car stability systems
Answer: a
Clarification: MEMS gyros are being exploited not only in avionic applications such as flight control, standby attitude and heading reference systems, and missile mid-course guidance but also in the automobile industry in car stability enhancement systems. Space launch vehicles use ring laser gyros which are more accurate.

2. Why is a tuning fork gyro better than the vibrating cylinder type gyro?
a) Reduce base motion
b) Low power consumption
c) Easy to manufacture
d) Low run up time
Answer: a
Clarification: The vibrating mass rate gyro is a simple instrument suffers from the unacceptable characteristic that the smallest linear motions applied to its base cause unacceptably large errors. To overcome the effect of base motion, it is necessary to use balanced oscillations in which the oscillations of one mass are counter-balanced by equal and opposite motion of a second equal mass as in the case of tuning fork gyro.

3. Which type of gyros works by calculating the difference in time taken by light to travel in a closed circle?
a) Ring laser gyro
b) MEMS gyro
c) Floated gyro
d) Dry tuned gyro
Answer: a
Clarification: Optical gyroscopes such as the ring laser gyro and the fibre optic gyro measure angular rate of rotation by sensing the resulting difference in the transit times for laser light waves travelling around a closed path in opposite directions.

4. What is the basic principle by which laser gyros work?
a) Coriolis effect
b) Conservation of momentum
c) Sagnac effect
d) Mass conservation
Answer: c
Clarification: The Sagnac effect is a relativistic phenomena of light in a rotating reference system. When laser beams circulate in a closed path that is rotating in an inertial space, the optical length seen by the co-rotating beam appears longer than that seen by counter rotating beam.

5. Which of the following type of gyro works by counting the nodes of standing waves of laser beams?
a) Ring laser gyro
b) Optical fiber gyro
c) Dry tuned gyro
d) Floated gyro
Answer: a
Clarification: In a Ring laser gyro, the counterpropagating beams form resonant nodes within the gyro cavity and create an electromagnetic standing wave that remains fixed with inertial space. When the housing of the gyro rotates, a detector can count nodes of the standing waves, each of which represents an angle.

6. A fiber optic gyro measures rotation using the _______ of the two beams?
a) Intensity difference
b) Resonance
c) Interference intensity
d) Wavelength difference
Answer: c
Clarification: In a fiber optic gyro, The counterpropagating beams are launched into an optical path and are recombined as they exit. The interference generated by the recombination depends on the optical phase difference between the two beams and therefore provides a measure of rotation.

7. In two mode RLGs, only linearly polarized modes can be resonant in the cavity.
a) True
b) False
Answer: a
Clarification: Two mode RLGs are planar by design so that only linearly polarized modes can be resonant in the cavity. Suppression of one of the two modes of polarization ensures stable operation.

8. The emission of photons by the gas medium that fills the RLG cavity is called as?
a) Laser discharge
b) Spontaneous discharge
c) Spontaneous emission
d) Laser emission
Answer: c
Clarification: The gas medium that supplies the gain for the laser also occasionally emits photons which are unrelated to the laser signal. This is known as spontaneous emissions are leads to noise and random walk in the RLG angle output.

9. What is the cause of lock-in phenomena in RLG?
a) Backscatter
b) Low intensity
c) High intensity
d) Low standing wave ratio
Answer: a
Clarification: Lock-in phenomenon leads makes the RLG insensitive to low angular rates. The cause of the lock-in phenomenon is backscatter within the cavity, usually resulting from imperfections in or particulates in the mirror surfaces.

10. Which method uses a turntable in RLG to reduce lock-in errors?
a) Intensity control
b) Rate biasing
c) Using mechanical dither
d) Random rate fixing
Answer: b
Clarification: The method of rate biasing employs a turntable that applies a constant rotation to the gyro. An angular encoder measures the relative angle between the instrument and its base.

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