Category: Avionics Objective Questions

Avionics Interview Questions and Answers on “Fly-By-Wire Technology – 2”.

1. What type of system is classified as “Direct electric link system”?
a) Systems with parallel wire connection
b) System with serial wire connection
c) System with motion sensor feedback
d) System without motion sensor feedback
Answer: d
Clarification: A FBW system by definition has to have a motion feedback system. Without these, the system is considered as “Direct electric system”. The information from these sensors is used to automatically stabilize the aircraft.

2. What does FBW use to scale the control surface deflection according to the aircraft’s airspeed and height?
a) Air Data Computer
b) Flight Management System
c) Flight Control Computer
d) Autopilot system
Answer: a
Clarification: FBW uses an Air Data System to scale the control surface deflection according to the aircraft’s airspeed and height variations. The need for air data information on the airspeed and height is to compensate for the very wide variation in the control surface effectiveness over the aircraft’s flight envelope of height and speed combinations. The Air Data Computer provides various information available from the airstream such as airspeed, altitude, and angle of attack.

3. What is the incidence angle in the yaw plane called?
a) Side slip angle
b) Yaw angle
c) Crossflow angle
d) Angle of crosswind
Answer: a
Clarification: The angle of incidence in the yaw plane is known as the side slip angle. It is the angle between the direction the aircraft is travelling and the direction its nose is pointing. When the side slip angle is high the aircraft is not in a coordinated turn and hence is flying inefficiently.

4. Why does an FBW system use a smaller tail area?
a) Bigger tails are harder to move as they produce larger wing loads
b) Actively controls the tail thus making up for the reduced stability due to lesser area
c) Tail does not contribute much to stability and its area can thus be reduced effectively
d) To reduce weight and drag but at a cost of natural stability
Answer: d
Clarification: The reason for using reduced tail area is to reduce weight, drag and to increase overall performance, But at a cost of reduced natural stability. A FBW makes up for the reduced stability by actively controlling the tailplane and rudder using accurate motion feedback sensors and actuators.

5. An aircraft is negatively stable when ______
a) its tailplane produces negative lift (downwards)
b) its tailplane produces positive lift (upwards)
c) its tailplane does not produce lift
d) it is flying inverted
Answer: b
Clarification: An aircraft is said to be negatively stable when its tailplane produces positive
lift. The tail of an aircraft without an FBW system must always produce negative lift to maintain stability and to keep the nose up. Since it produces negative lift, it actually acts in the direction of weight reducing aerodynamic efficiency. In an FBW equipped aircraft a positive lift producing tail can be used by using flight control computers and motion sensors to main stability at all times.

6. A highly stable aircraft is not easily maneuverable.
a) True
b) False
Answer: a
Clarification: An aircraft is said to be stable when the aerodynamic forces on the aircraft are equal to thrust produced and the weight of the aircraft. Such a condition is called steady level flight. A highly stable aircraft will return to its initial stable position even if disturbed. Maneuverability is the rate of pitch, roll, and yaw an aircraft can execute without failing. Roll, pitch, and yaw are basically disturbances and a stable aircraft will try to resist the change from its initial position.

7. A FBW control stick is referred as _______
a) FBW joystick
b) FBW control pad
c) FBW inceptor
d) FBW analog stick
Answer: c
Clarification: A FBW control stick is referred to as FBW inceptor. An inceptor by definition is a device that converts the pilot’s control inputs into electrical signals. There are two types of inceptors- active and passive.

8. Why are dampers an essential element in FBW inceptors?
a) Control aircraft stability by damping forces
b) Acts as a low pass filter on the stick movement
c) Provides accurate deflections
d) To prevent aircraft to carry out critical maneuvers
Answer: b
Clarification: Without the damper, the stick would be considerably under damped because of the low friction in the mechanism and the significant mass of the hand grip. It provides a smooth feel to the stick movement; the spring–mass–damper combination acting as a low pass filter on the stick movement. These characteristics are carefully tailored to meet the consensus of pilot approval.

9. FBW has the power to reject pilot inputs in extreme situations.
a) True
b) False
Answer: a
Clarification: FBW system automatically limits the pilot’s commands to ensure it does not enter unacceptable altitude or approach stall. A number of aircraft are lost in a year due to flying too close to their maneuver limits and the very high workload in the event of a subsequent emergency. This system makes a significant contribution to flight safety.

10. What is the relation between autopilot and FBW?
a) FBW provides autopilot commands for roll, pitch, and yaw
b) Autopilot provides FBW commands of roll, pitch, and yaw
c) Autopilot is a part of FBW system
d) Autopilot is not related to FBW
Answer: b
Clarification: The autopilot is like an artificial pilot system which flies the aircraft under a set of constraints. It provides steering commands such as roll, pitch and yaw rates to the FBW system. FBW system ensures that response to the autopilot commands is fast and well damped, providing smooth control of aircraft in autopilot modes.

11. Fill the missing block in the roll rate command system.

a) Rate gyro
b) Flight control computer
c) Display
d) Autopilot
Answer: a
Clarification: The missing block is in a feedback loop, typically it consists of a motion sensor. Here the motion sensor used is a rate gyro. The signal from the rate gyro is subtracted from pilot’s input so that the error in deflection is corrected.

12. Why is FBW essential in stealth aircraft?
a) FBW system damps radar energy
b) Improves control
c) Reduces engine noise
d) Disturbs tracking techniques used by missiles
Answer: b
Clarification: Stealth configurations and requirements can conflict with aerodynamics requirements and FBW flight control is essential to give acceptable control and safe handling across the flight envelope. An example of such is the American fighter F -117, nicknamed “Nighthawk”. It is almost impossible to fly this aircraft without feedback FBW system.

Avionics for Interviews,

Avionics Multiple Choice Questions on “Communication Receivers”.

1. Which of the following are the two main characteristics of receivers?
a) Selectivity and sensitivity
b) Gain and attenuation
c) Modulation and demodulation
d) Multiplexing and demultiplexing
Answer: a
Clarification: A communication receiver must be able to identify and select the desired signal from thousands of others present in the frequency spectrum (selectivity) and to provide sufficient amplification to recover the modulating signal (sensitivity). A receiver with good selectivity will isolate the desired signal in the RF spectrum and eliminate or at least greatly attenuate all other signals.

2. What circuit provides the initial selectivity in a receiver?
a) Amplifier
b) Attenuator
c) Multiplexer
d) LC tuned circuits
Answer: d
Clarification: Initial selectivity in a receiver is normally obtained by using LC tuned circuits. By carefully controlling the Q of the resonant circuit, we can set the desired selectivity.

3. The ability to pick up week signals by a receiver is called _________
a) Gain
b) Amplification
c) Sensitivity
d) Selectivity
Answer: c
Clarification: A communication receiver’s sensitivity, or ability to pick up weak signals, is mainly a function of overall gain, the factor by which an input signal is multiplied to produce the output signal. In general, the higher the gain of a receiver, the better its sensitivity.

4. What is the input signal level that is approximately equal to the average internally generated noise value called?
a) MDS
b) MBS
c) MMD
d) MSD
Answer: a
Clarification: The MDS or Minimum Discernible Signal is the input signal level that is approximately equal to the average internally generated noise value. This noise value is called the noise floor of the receiver. MDS is the amount of signal that would produce the same audio power output as the noise floor signal. The MDS is usually expressed in dBm.

5. Analog signals : Signal to noise ratio:: Digital signals _________
a) Signal Attenuation
b) Bit error rate
c) Error rate
d) Digital noise ratio
Answer: b
Clarification: For analog signals, the signal-to-noise ratio is the main consideration in analog signals. For digital signal transmission, the bit error rate (BER) is the main consideration. BER is the number of errors made in the transmission of many serial data bits.

6. A sensitive and selective receiver can be made using only amplifiers, selective filters, and a demodulator.
a) True
b) False
Answer: a
Clarification: A sensitive and selective receiver can be made using only amplifiers, selective filters and a demodulator. This is called a tuned radio frequency or TRF receiver. Early radios used this design. However, such a receiver does not usually deliver the kind of performance expected in modern communications applications.

7. What type of receivers converts all incoming frequency into a lower frequency for better selectivity and sensitivity?
a) Analogous receivers
b) Superheterodyne receivers
c) Digital receiver
d) Crystal receiver
Answer: b
Clarification: Superheterodyne receivers convert all incoming signals to a lower frequency, known as the intermediate frequency (IF), at which a single set of amplifiers and filters is used to provide a fixed level of sensitivity and selectivity. Most of the gain and selectivity in a superheterodyne receiver are obtained in the IF amplifiers.

8. What is the output of a mixer circuit?
a) Sum of frequencies
b) Difference of frequencies
c) Sum and difference of frequencies
d) Multiplication of frequencies
Answer: c
Clarification: The key circuit is the mixer, which acts as a simple amplitude modulator to produce sum and difference frequencies. The incoming signal is mixed with a local oscillator signal to produce this conversion.

9. What is connected between the antenna and the mixer to avoid oscillator radiation?
a) LNA
b) Attenuator
c) Duplexer
d) Power amplifier
Answer: a
Clarification: LNA or low noise amplifier is placed in between the antenna and the mixer. The oscillator signal is relatively strong and some of it can leak through and appear at the input of the mixer. The RF amplifier between the mixer and the antenna isolates the two, significantly reducing any local oscillator radiation.

10. Which of the following is not an advantage of using RF amplifiers in the initial stage of signal selection?
a) Low noise
b) Reduced oscillator radiation
c) Better selectivity
d) Less power consumption
Answer: d
Clarification: The use of RF amplifiers in the initial stage of signal selection reduces the effect of noise.RF amplifiers improve sensitivity, because of the extra gain; improve selectivity, because of the added tuned circuits; and improve the S/N ratio. Further, spurious signals are more effectively rejected, minimizing unwanted signal generation in the mixer.

11. The LNA of a transducer has failed during the transmission of a signal. Which component’s failure has caused this?
a) Duplexer
b) RF amplifier
c) Antenna
d) Mixer
Answer: a
Clarification: A duplexer is a device which acts as a switch and stops the high power transmission signals from entering into the receiver, which is tuned to handle very low power for better sensitivity. When the duplexer fails, the high power signals enter the receiver where the Low noise amplifier is damaged.

12. What type of oscillators are used to input a wide range of frequencies to the IF amplifier?
a) LC oscillators
b) Crystal oscillators
c) Variable frequency oscillators
d) Diode oscillators
Answer: c
Clarification: The local oscillator is usually a variable frequency oscillator or a frequency synthesizer so that its frequency can be adjusted over a relatively wide range. As the local-oscillator frequency is changed, the mixer translates a wide range of input frequencies to the fixed IF.

Avionics Multiple Choice Questions on “Satellite Applications”.

1. What is the primary use of communication satellites?
a) Telephone service
b) Surveillance
c) Research
d) GPS
Answer: a
Clarification: The primary use of communication satellites is in long-distance telephone service. Satellites greatly simplify long-distance calls not only within countries but also worldwide.

2. Which of the following is not a reason for redistributing TV signals through satellites rather than skywaves or spacewaves?
a) High frequency signal
b) Long distance communication
c) Economically feasible
d) Power requirements
Answer: d
Clarification: TV signals are being transmitted through satellites for redistribution. Because of the very high-frequency signals involved in TV transmission, other long-distance transmission methods are not technically or economically feasible.

3. What type of satellite TV service uses compressed data transmission to beam signals directly to every home?
a) Direct broadcast satellite
b) Mobile satellite service
c) Broadcasting satellite service
d) Fixed satellite service
Answer: a
Clarification: The direct broadcast satellite (DBS) system is an all-digital system. Data compression techniques are used to reduce the data rate in order to produce high-quality picture and sound. They uses special broad coverage satellites with high power to transmit cable-TV-like services direct to homes equipped with the special DBS receivers.

4. Which frequency band does the direct broadcast satellite system use?
a) C band
b) X band
c) Ku band
d) MF band
Answer: c
Clarification: The DBS satellite uses the Ku band with a frequency range of 11 to 14 GHz. Uplink signals are usually in the 14- to 14.5-GHz range, and the downlink usually covers the range of 10.95 to 12.75 GHz.

5. What technique does DSP use to double the number of channels by using helical antennas?
a) Spatial isolation
b) Frequency reuse
c) Multiplexing
d) Modulation
Answer: b
Clarification: The digital signal is transmitted from the satellite to the receivers using circular polarization. The DBS satellites have right-hand and left-hand circularly polarized (RHCP and LHCP) helical antennas. By transmitting both polarities of signal, frequency reuse can be incorporated to double the channel capacity.

6. What is the number of satellites present in the Iridium system?
a) 72
b) 51
c) 66
d) 32
Answer: c
Clarification: The satellite systems use low-earth-orbit satellites to perform the relay services to the main telephone system or to make a connection directly between any two cellular telephones using the system. One of the oldest and most widely used is the Iridium system. It uses a constellation of 66 satellites in six polar orbits with 11 satellites per orbit 420 mi above the earth.

7. Which frequency band is used for connecting the satellite system with the public switched telephone network?
a) L band
b) Ku band
c) C band
d) Ka band
Answer: d
Clarification: The satellites communicate with ground stations called gateways that connect the system to the public switched telephone network. The satellites also communicate among themselves. Both gateway and intersatellite communication takes place over Ka band frequencies.

8. What provides the sufficient drive to the final power amplifier?
a) Intermediate-power amplifier
b) Operational amplifier
c) Power driver circuit
d) Up converter
Answer: a
Clarification: The power amplifier usually begins with an initial stage called the intermediate-power amplifier (IPA). This provides sufficient drive to the final high-power amplifier (HPA).

Avionics Multiple Choice Questions on “Pressure Measurements”.

1. The different probes that disturb the airflow is called ______
a) Air data probe
b) Data probe
c) Intrusive probe
d) Static probes
Answer: c
Clarification: All of the sensing probes, except for the flush mounted static probe, are intrusive because they disturb the local flow over the body of the aircraft. Thus they are also called intrusive probes.

2. The absolute pressure of the still air surrounding the aircraft is called as______
a) Static pressure
b) Stagnation pressure
c) Constant pressure
d) Absolute pressure
Answer: a
Clarification: static pressure is the pressure of the still air surrounding the aircraft body even when the aircraft is moving. It is measured using static ports placed along the aircraft skin.

3. Where are self-aligning pitot tubes used?
a) Bomber planes
b) Commercial airliners
c) High angle of attack fighter aircraft
d) General aviation
Answer: c
Clarification: When the angle of attack and the sideslip angle are under 10°, they do not affect the pressure measurements much. In applications such as high angle of attack fighters, special self-aligning pitot tubes are used to measure the stagnation pressure.

4. What is the difference between the actual free stream pressure and the measured static pressure called?
a) Static error
b) Static defect
c) Free stream error
d) Dynamic pressure
Answer: b
Clarification: The pressure that is sensed via the pitot-static port will be different from the actual free stream pressure due to the interference from the skin, angle of attack and the sideslip angle. This difference is referred to as the static defect.

5. Which of the following is done to reduce the static defect?
a) Streamlined configuration of the whole aircraft
b) Less weight as payload
c) Wind tunnel tests to find spots of body-flow interference
d) Deploy Flaps and slats
Answer: c
Clarification: Various wind tunnel tests are done to predict the optimum location for the static port so that the interference of the flow with the body is minimum. Since static defect is predictable, it can be corrected in the air-data computer.

6. What are the tubes in the aircraft that carry the air pressure to the instruments is called as?
a) Pneumatic plumbing
b) Pressure lines
c) Pressure tubes
d) Blue lines
Answer: a
Clarification: Pipes that carry the air pressure sensed from the pitot tube or the pitot-static tube to the air data computer and the various other flight instruments such as the airspeed indicator, altitude indicator and the vertical speed indicator is collectively referred to as pneumatic plumbing.

7. What is the difference between the static pressure and the stagnation pressure when the aircraft is stationary?
a) Infinite
b) Any random value
c) No difference
d) Static pressure
Answer: d
Clarification: when the aircraft is stationary, the pressure sensed by the static port is the free stream air pressure and the stagnation pressure ports are zero. Since the aircraft is not moving stagnation pressure is zero and hence the difference between the two values is the static pressure.

8. The impact pressure and the dynamic pressure are the same.
a) True
b) False
Answer: b
Clarification: Both impact and dynamic pressures are the difference between the stagnation and the static pressure but impact pressure is the dynamic pressure with compressibility effects taken into account.

9. At supersonic speeds, a normal pitot tube cannot be used for speed measurements.
a) True
b) False
Answer: a
Clarification: At supersonic speeds, the pressure sensed inside the pitot tube is ideally the pressure after the formation of shock waves inside the tube. Hence the value of stagnation pressure is different from that actually experienced by the aircraft.

10. Which of the following instruments use the pitot-static probe for its input?
a) Airspeed indicator
b) Altitude indicator
c) Vertical speed indicator
d) Attitude indicator
Answer: d
Clarification: The instruments that use pitot-static probe are airspeed indicator, altitude indicator or the altimeter and the vertical speed indicator. The attitude indicator uses the gyro to measure the orientation of the aircraft.

Avionics Multiple Choice Questions on “Carrier Landing Systems”.

1. The relative speed of the aircraft with respect to the carrier deck is _________
a) Lower
b) Greater
c) Zero
d) Indifferent
Answer: a
Clarification: Jet aircraft approach the carrier deck with at airspeeds up to 125 knots. Their speed relative to the deck is lower due to the “wind over the deck,” which is normally about 30 knots.

2. What is the inclination of the glide slope with respect to the moving flight deck?
a) 3°
b) 5°
c) 3.5°
d) 4°
Answer: d
Clarification: The approach path, often called the glide slope, is in the vertical plane containing the runway center line and is inclined 3.5° relative to the sea at the touchdown point and 4° relative to the moving flight deck.

3. Which of the following causes a “burble” at the threshold and along the glide path?
a) High speed landings
b) Low visibility
c) Heaving motion of ship
d) Steady state wake
Answer: d
Clarification: Steady state wake caused by the relative wind over the ship’s deck and around the superstructure, Which causes a “burble” at the threshold and the glide path.

4. Wake perturbations are caused by ________
a) High speed landings
b) Low visibility
c) Heaving motion of ship
d) Steady state wake
Answer: c
Clarification: Wake perturbations, due to the ship’s angular motions and heave, causing fluctuations with standard deviations of 2 ft/sec(horizontal) and 4 ft/sec (vertical) about the steady state wake.

5. Aircraft executing missed approach from low altitude is called as ____________
a) Bolter
b) Faultie
c) Ranger
d) Dropper
Answer: a
Clarification: An aircraft executing a missed approach from low altitude is called a bolter. Bolters fly to a Tacan- defined holding point that moves with the aircraft carrier.

6. The ACLS can land an aircraft in zero visibility conditions.
a) True
b) False
Answer: a
Clarification: The ACLS is capable of landing an aircraft “hands-off,” giving the U.S. Navy an operational capability in zero visibility conditions. It can land an airplane more accurately than an average pilot.

7. Which of the following is an optical landing aid used in aircraft carriers?
a) ACLS
b) FLOLS
c) SPN-41
d) SPN-46
Answer: b
Clarification: FLOLS or the Fresnel lens optical landing system consists of an array of 5 Fresnel lens showing the pilot a yellow spot that moves relatively to a lighted green horizontal reference bar.

8. Why is heave motion of the carrier not corrected in the FLOLS?
a) Two aircraft use simultaneously
b) Atmospheric fluctuations
c) Too random motion
d) Not economical
Answer: a
Clarification: Lens pointing angles can be adjusted to a quadratic function of heave and can be compensated. This compensation is not implemented because the “meatball” is often shared by two aircraft on final approach simultaneously.

9. What is the frequency band used by the ACLS?
a) Ka band
b) S band
c) C band
d) E band
Answer: a
Clarification: Two electronic instrument landing systems are found o all large U.S. carriers. Th ACLS involves two identical conically scanned Ka band radars set aft of the island about 125 and 135ft above the water line.

10. Which of the following is false with respect to ACLS?
a) Zero visibility landing is possible
b) Uses Ka band radars
c) Compensated for carrier roll, heave and pitch
d) Only handle one aircraft at a time
Answer: d
Clarification: The two identical conically scanned radar antennas can track two aircraft simultaneously and, if desired, can uplink guidance signals to autopilots.

11. What is added to SPN-42 to eliminate wandering of the echo skin?
a) AESA
b) Aircraft beacon
c) PESA
d) Helical antenna
Answer: b
Clarification: The SPN-42 was retrofitted with a small X-band parabola when aircraft beacons were added to eliminate errors caused by wandering of the echo skin.