Category: Avionics Objective Questions

Avionics Multiple Choice Questions on “Electronic Scanned Array Radar”.

1. What is the fundamental limitation of the radar that is overcome by Electronic scanned array radars?
a) More clarity
b) Situation awareness
c) Better range
d) Less noise
Answer: b
Clarification: The fundamental limitation in military radars is situation awareness. This limitation is overcome by the electronically scanned array which has a very high rate of scanning.

2. How is the radar beam moved in the ESA?
a) Phase shift
b) Mechanical gimbal
c) Mechanical servos
d) Hydraulics
Answer: a
Clarification: In ESA, the antenna’s beam is moved electronically by setting the phase angles of phase shifters located at each radiating element to provide a linear phase taper across the array surface.

3. Which of the following determines the direction of the antenna beam in ESA?
a) Physical direction of antenna
b) Direction of aircraft nose
c) Slope of the phase taper
d) Mechanical gimbal
Answer: c
Clarification: The ESA controls the beam by phase shifters. The slope of the phase taper determines the direction in which the antenna beam will be pointed.

4. The ESA radar beam can be repositioned in a few _______
a) Microseconds
b) Nanoseconds
c) Milliseconds
d) Seconds
Answer: a
Clarification: Since the antenna’s phase shifter settings can be changed in a few microseconds, an ESA’s beam can be repositioned almost instantly.

5. The ESA is more _________ since it has no moving parts.
a) Prone to failure
b) Powerful
c) Reliable
d) Accurate
Answer: c
Clarification: The antenna reliability is dramatically improved in an ESA since there is no moving parts present. The antennas face one direction but the radar beam can be steered electronically to a very wide angle.

6. Which of the following are present in an ESA?
a) Gimbals
b) Electronic motors
c) Phase shifter
d) Potentiometer
Answer: c
Clarification: The ESA has no mechanical moving parts, such as antenna gimbals, potentiometers, rotary joints, or hydraulic/electronic motors. It uses phase shifters to electronically steer the beam.

7. Both AESA and PESA are ________ radars?
a) Pulse
b) Continuous wave
c) Low frequency
d) Analog
Answer: a
Clarification: Both AESA and PESA that are currently in use are pulse radars. Its basic principle is that shorts bursts of radio pulse are emitted which reflect off a target and the reflected pulse gives the information about the object.

8. Which of the following is false with respect to PESA?
a) PESA can only have one main beam and one transmit power source
b) All elements combine to a single receiver. Each element steers the beam through phase shifters
c) Because it uses a, multiple frequencies, it is less susceptible to enemy jammers
d) PESA is more technically simple
Answer: c
Clarification: In a PESA only one transmitter drives the whole antenna and hence only one frequency can be achieved at a time. This allows it to be more susceptible to jammers.

9. What is the number of transmitting modules in a common AESA?
a) 20 to 50
b) 1000 to 2000
c) 150 to 200
d) 1
Answer: b
Clarification: A typical airborne active array contains 1000 to 2000 transmitting modules, each capable of transmitting 5 to 20 watts of power.

10. Which one of the following is common between AESA and PESA?
a) Number of transmitting modules
b) Number of frequencies that can be used
c) Power required by each transmitter
d) Electronic scanning capability
Answer: d
Clarification: One of the basic common features between the AESA and PESA is that both provide electronic scanning. This allows the use of narrow beams since the rate of scanning is very high.

11. AESA is more reliable than PESA.
a) True
b) False
Answer: a
Clarification: An AESA solves many of the reliability and maintainability problems due to TWT and power supply problems. 4 to 6% of the T/R module could fail without noticeable degradation in antenna performance.

12. AESA can alter its transmitting and receiving patterns.
a) True
b) False
Answer: a
Clarification: In AESA a new control variable is introduced. The gain of each Tx and Rx module can be controlled and hence the array radars can adaptively alter their transmit and receive antenna pattern to maximize system performance.

13. Which of the following can track multiple targets with ease?
a) AESA
b) PESA
c) ESA
d) Conical radar antenna
Answer: a
Clarification: AESA radars can produce multiple radar frequencies with multiple beams. This allows the radar to have faster scan rates and can track multiple targets with ease.

14. The possibility of one phased array radar to act as multiple radars is called as _______
a) ESA
b) Multimode
c) Digital
d) interleaving radar modes
Answer: d
Clarification: Beam agility makes it possible for one phased array radar to act as multiple radars each with its own beam shape and scan pattern! This is referred to as interleaving radar modes. The same radar can be tracking for airborne threats using one beam shape and scan pattern while searching for ground targets using another beam shape and scan pattern.

15. In an aircraft ESA the beam shape and direction is controlled by _______
a) Navigator
b) Computer
c) Ground controller
d) Cannot be controlled
Answer: b
Clarification: The beam shape and direction is controlled by an on-board computer which gives the necessary phase shift to the phase shifters to change the beam direction and shape.

Avionics Multiple Choice Questions on “Digital Implementation”.

1. How does the digital implementation in the FBW system reduce weight?
a) Lightweight materials
b) Fewer components
c) System integration
d) Automated control
Answer: c
Clarification: In a typical Digital FBW system, One computer can control all three axes of control, whereas an analog system requires dedicated hardware for each axis of control. The reduction in hardware weight and volume, due to system integration, is of the order of 5:1 for a system of even modest complexity. The more complex systems could not be implemented economically using analogue technology.

2. Which of the following is not a result of digital implementation?
a) Hardware economy
b) Flexibility in updating
c) More power
d) Built in test capabilities
Answer: c
Clarification: The digital implementation in FBW only affects the control and stability of the aircraft. Power is not, in any way, related to the FBW system.

3. What is it called when the sampled signal is of lower frequency than the original signal?
a) Aliasing
b) Overshoot
c) Steady state error
d) Damping
Answer: a
Clarification: When the sampled signal is of lower frequency than the original signal it is known as aliasing. Aliasing induces data loss and errors. It can be reduced by a process called anti-aliasing.

4. How is aliasing prevented?
a) Sampling at the same frequency of the original signal
b) Sampling at double the frequency of the original signal
c) Sampling at less than double the frequency of the original signal
d) Sampling at more than double the frequency of the original signal
Answer: d
Clarification: Aliasing occurs when the sampling rate is lower than the frequency of the original signal. The Nyquist theorem states that the sampling rate should be more than twice the frequency of the original signal to avoid aliasing.

5. How is data staleness overcome?
a) Time synchronisation
b) Down conversion
c) Up conversion
d) Using multiple channels
Answer: a
Clarification: Data staleness problem it is necessary to have some form of time synchronisation of the computer iteration periods. This iteration period synchronisation is generally implemented through software.

6. Which of the following is not an advantage of using a digital data bus?
a) Self test
b) Multiplexing
c) less weight
d) Not affected by electromagnetic interference
Answer: d
Clarification: Very large reductions in the weight of cabling are achieved by the use of multiplexed data transmission and data bus networks. High integrity data transmission can be achieved with very comprehensive self checking and data validation capabilities. However, they are heavily affected by electromagnetic interference.

7. What happens when the output of one channel is delayed by one iteration period before comparing with other channels in a quadruplex system?
a) Latency
b) Staleness
c) Aliasing
d) High noise
Answer: b
Clarification: Data staleness occurs when a channel is delayed by, say, one iteration, before comparison with others. To overcome this problem it is necessary to have some form of time synchronisation of the computer iteration periods.

8. Which of the following is true with respect to the passive optical sensor?
a) Not affected by EMI
b) Does not require an electrical supply
c) Output from the sensor is an optical signal
d) Processing this signal does not require any electrical device
Answer: d
Clarification: Passive optical sensors offers particular advantages as these sensors are not affected by EMI. Passive optical sensors are defined as sensors which do not require electrical supplies or any electronic processing at the sensor, the output of the sensor being an optical signal which is modulated by the quantity being measured. The processing of this optical signal is carried out by a separate electronic unit which is fully screened from EMI, the only connection between the sensor and the electronic unit being an optical fibre cable.

Avionics Multiple Choice Questions on “Pulse Code Modulation”.

1. Which of the following type of multiplexing uses pulse code modulation?
a) Frequency division multiplexing
b) Time division multiplexing
c) Code division multiplexing
d) Amplitude limited multiplexing
Answer: b
Clarification: The most popular form of TDM uses pulse-code modulation (PCM), in which multiple channels of digital data are transmitted in serial form. Each channel is assigned a time slot in which to transmit one binary word of data. The data streams from the various channels are interleaved and transmitted sequentially.

2. Which of the following statements is true with respect to PCM?
a) The parallel binary data is converted into serial before transmission
b) Analog data is transmitted directly
c) Analog signal is amplified before transmission
d) The analog signal is converted into parallel binary data before transmission
Answer: a
Clarification: The analog signal is converted into a digital signal. Since the converted digital signal is parallel bits of data, it has to be converted to serial before it can be multiplexed and transmitted.

3. Which of the following is false with respect to PCM?
a) Reliable
b) Inexpensive
c) Resistant to noise
d) Not easily recoverable
Answer: d
Clarification: When signals have been degraded because of noise, attenuation, or distortion, all the receiver has to do is to determine whether a pulse was transmitted. Amplitude, width, frequency, phase shape, and so on do not affect reception. Thus PCM signals are easily recovered and rejuvenated, no matter what the circumstances.

4. A special PCM system uses 16 channels of data, one whose purpose is identification (ID) and synchronization. Find (a) the number of available data channels.
a) 15
b) 16
c) 14
d) 18
Answer: a
Clarification: 16 (total no. of channels) – 1 (channel used for ID) = 15 (for data).

5. A special PCM system uses 16 channels of data, one whose purpose is an identification (ID) and synchronization. The word length is 6 bits. Find the number of bits per frame.
a) 94
b) 95
c) 96
d) 125
Answer: c
Clarification: Here, Data channels = 16 and word length is 6 bits.
Bits per frame = 6 x 16 = 96.

6. A special PCM system uses 16 channels of data, one whose purpose is an identification (ID) and synchronization. The sampling rate is 3.5 kHz. The word length is 6 bits. Find the serial data rate.
a) 451kHz
b) 326kHz
c) 152kHz
d) 336kHz
Answer: d
Clarification: Serial data rate = sampling rate x no. bits/frame = 3.5 kHz x 96 = 336 kHz.

7. All local and long-distance connections are digital.
a) True
b) False
Answer: a
Clarification: All modern telephone systems use digital transmission via PCM and TDM. The only place where analog signals are still used is in the local loop—the connection between a telephone company’s central office (CO) and the subscriber’s telephone, known as the customer premises equipment (CPE). All local and long-distance connections are digital.

8. In a TDD one channel is sufficient for transmission.
a) True
b) False
Answer: a
Clarification: Time-division duplexing (TDD) means that signals are transmitted simultaneously on a single channel by interleaving them in different time slots. Each time slot may contain one data word, such as 1 byte from an A/D converter or a D/A converter. As long as the serial data rate is high enough, a user will never know the difference. The primary benefit of TDD is that only one channel is needed. It saves spectrum space and cost.

Avionics Multiple Choice Questions on “Navigation Equations”.

1. The navigation equations are used by the on-board computer to calculate position velocity and altitude.
a) True
b) False
Answer: a
Clarification: The navigation equations how the sensor outputs are processed in the on-board computer in order ti calculate the position, velocity and attitude of the aircraft. The navigation equations contain instructions and data and are part of the airborne software that also includes moding, display drivers, failure detection and an operating system.

2. Which one of the following is not an input utilized by the aircraft navigation system?
a) Sonar
b) Radio aids
c) Dead reckoning data
d) Celestial measurements
Answer: a
Clarification: The navigation system utilizes three types of sensor information: position data from radio aids, radar and satellites; Dead reckoning data from inertial sensors; Line of sight direction to stars or celestial measurements.

3. What is the angle between the normal to the reference ellipsoid and the equatorial plane at a point called?
a) Geodetic angle
b) Correction factor
c) Geodetic latitude
d) Earth angle
Answer: c
Clarification: Geodetic latitude of a point is the angle between the normal to the reference ellipsoid and the equatorial plane. Geodetic latitude is our usual understanding of map latitude.

4. Which of the following is false with respect to Earth centered inertial coordinate system?
a) Accuracy is 10^-5/hr
b) Newton’s laws are not valid
c) Angular coordinates of stars are conventionally tabulated in ECI
d) Used in mechanizing inertial navigators
Answer: b
Clarification: The Earth centered coordinate system has three navigational functions. First, Newton’s laws are valid in any ECI coordinate frame, Second, the angular coordinates of stars are conventionally tabulated in ECI. Third, they are used in mechanizing inertial navigators.

5. Which coordinate system is used in satellite based radio navigation?
a) Earth centered, Earth fixed
b) Earth centered inertial
c) Geodetic spherical coordinates
d) Geodetic wander azimuth
Answer: a
Clarification: Satellite based radio navigation system uses ECEF coordinated to calculate satellite and aircraft position. The origin is at the mass center of the earth and its axis lies along the earth’s spin axis.

6. Geocentric spherical coordinates are used for short range dead reckoning navigation.
a) True
b) False
Answer: a
Clarification: Geocentric coordinates are sometimes mechanized in short range dead reckoning systems using spherical earth approximation. These are the spherical coordinates of the radius vector R.

7. What is the technique of calculating position from measurements of velocity called?
a) Dead reckoning
b) Doppler radar
c) Secondary surveillance
d) Celestial navigation
Answer: a
Clarification: Dead reckoning is the technique of calculating position from the measurements of velocity. It is the means of navigation in the absence of position fixes and consists in calculating the position by extrapolating measured ground speed.

8. The angle of arrival, relative to the airframe, of a radio signal from an external transmitter is called _________
a) Bearing
b) Heading
c) Phase
d) Approach angle
Answer: a
Clarification: The angle of arrival, relative to the airframe, of a radio signal from an external transmitter is called bearing. Bearing is measured by the difference in phase or time of arrival at multiple antennas on the airframe.

9. ________ related ranging errors to the dispersion in measured position?
a) GEOP
b) GDCP
c) GDOP
d) APEG
Answer: c
Clarification: GDOP or Geometric Dilution of Precision relates ranging errors to the dispersion in measured position. If three range measurements are made in the orthogonal direction, the standard deviation in the aircraft’s position error is the same as those of the three range sensors.

10. What is TDOP?
a) Time Dilution of pseudorange
b) Time Dilution of position
c) Time Dilution of pressure
d) Time Distortion of position
Answer: b
Clarification: TDOP is the Time Dilution of position. It is the contribution of clock error to the error in pseudorange.

Avionics Multiple Choice Questions on “Air Data Computers”.

1. ______ is used for setting stabilizer position and high speed performance boundaries?
a) Mach number
b) True airspeed
c) Calibrated airspeed
d) Altitude
Answer: a
Clarification: 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.

2. Which of the following does not come under air data computer?
a) Pressure ports
b) Pressure transducers
c) Computer
d) Output drivers for interfacing
Answer: a
Clarification: 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.

3. An air data computer can be used in multiple aircraft.
a) True
b) False
Answer: a
Clarification: The CADC includes program pin status which is designated connector pins that allow a standard CADC to serve in more than one aircraft. Thus, pin i could recognize that the installation is in the aircraft I, thereby activating its own pitot correction algorithm.

4. Which one of the following is not a part of the processor subassembly?
a) CPU
b) Volatile RAM
c) Non volatile RAM
d) Non erasable ROM
Answer: d
Clarification: 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.

5. Which of the following includes A/D conversions and packing of discrete signals into logical words?
a) Input processing
b) Output processing
c) Signal processing
d) Mainframe processor
Answer: a
Clarification: Input processing usually involves A/D conversion and packing of discrete signals into logic words, plus implementation of special serial data interfaces.

6. Which system has replaced the CADC by using smaller and cheaper microprocessors?
a) Navigational system
b) Distributed air data system
c) FADEC
d) Inertial system
Answer: b
Clarification: 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.

7. A distributed air data system uses a centralized flight control computer for calculations.
a) True
b) False
Answer: a
Clarification: A distributed air data system provides corrected pressure, temperature, and angle of attack data to a centralized flight control computer that computes altitude, mach, calibrated and true airspeed.

8. Which of the following is not an advantage of distributed air data system?
a) Elimination of pneumatic plumbing
b) Reliability
c) Easy maintenance
d) Better accuracy
Answer: d
Clarification: 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.

9. Distributed air data system reduces the overall weight of the aircraft.
a) True
b) False
Answer: a
Clarification: CADC uses long tubing from the probes to the CADC for the transfer of pressure data whereas distributed air data system transmits the data via electric wires. Electric wiring weighs less than tubing and the electrical transmission of pressure information eliminate lags.

10. Which one of the following is not an advantage of centralized architecture?
a) Simple design
b) Software is easily coded
c) Computer is readily accessible
d) Software is flexible
Answer: d
Clarification: 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.