This set of Avionics Multiple Choice Questions & Answers (MCQs) focuses on “ILS/MLS Coupled Landing System and Automatic Landing – 1”.
1. What is ILS?
a) Instrument landing system
b) Indian Levitation System
c) Indian Landing system
d) International Levitation system
Explanation: ILS or instrument landing system is a radio based approach guidance system installed at major airports and airfields where the runway length exceeds 1800 m which provides guidance in poor visibility conditions during the approach to the runway.
2. Which one of the following can provide reliable and accurate approach path guidance in category II visibility conditions?
Explanation: SBAS or Satellite Based Augmentation Systems exploiting differential GPS techniques will be able to provide reliable and accurate approach path guidance in category II visibility conditions. This will be increasingly used in the future.
3. What are the two main components of an ILS on the ground?
a) Horizontal alignment transmitter and vertical alignment transmitter
b) Localizer transmitter and glide slope transmitter
c) Center line transmitter and glide slope transmitter
d) Center line transmitter and approach slope transmitter
Explanation: ILS system basically comprises a localiser transmitter and a glide slope transmitter located by the airport runway together with two or three radio marker beacons located at set distances along the approach to the runway. The airborne equipment in the aircraft comprises receivers and antennas for the localiser, glide slope and marker transmissions.
4. What is the frequency used by the localizer transmitter?
Explanation: The localizer transmitter used VHF range from 108-122 MHz frequency and provides information to the aircraft as to whether it is flying to the left or right of the center line of the runway it is approaching. The localiser receiver output is proportional to the angular deviation γL, of the aircraft from the localiser beam center line which in turn corresponds to the center line of the runway.
5. What is the frequency used by the glide slope transmitter?
Explanation: The glide slope or glide path transmission is at UHF frequencies from 329.3 to 335 MHz frequency and provides information to the aircraft as to whether it is flying above or below the defined descent path of nominally 2.5◦, for the airport concerned. The glide slope receiver output is proportional to the angular deviation γV , of the aircraft from the center of the glide slope beam which in turn corresponds with the preferred descent path.
6. The use of autopilot for landing using ILS does not depend on _______
a) Visibility category
b) ILS ground installation standard
c) Runway lighting installation
d) Weight of the aircraft
Explanation: The height limits and visibility conditions in which the autopilot can be used to carry out a glide slope coupled approach to the runway depends on the visibility category to which the autopilot system is certified for operation, the ILS ground installation standard, the runway lighting installation and the airport’s runway traffic control capability.
7. Under what category does zero visibility conditions come?
a) Category I
b) Category II
c) Category III
d) Category IV
Explanation: Visibility conditions are divided into three categories, namely Category I, Category II and Category III, depending on the vertical visibility ceiling and the runway visual range (RVR). Category III includes zero visibility conditions.
8. What is DH?
a) Distance Height
b) Direct Height
c) Decision Height
d) Direction height
Explanation: This minimum permitted ceiling for vertical visibility for the landing to proceed is known as the decision height or DH. A very high integrity autopilot system is required for fully automatic landing below a DH of 100 ft – Cat. III conditions.
9. What is the frequency of marker beacon transmission?
a) 100 MHz
b) 75 MHz
c) 1 GHz
d) 1000 MHz
Explanation: The marker beacon transmissions are at 75 MHz. The middle marker beacon is located at a distance of between 1,000 and 2,000 m from the runway threshold and the outer marker beacon is situated at a distance of between 4,500 and 7,500 m from the middle marker.
10. MLS has a wide selection of channels to avoid interference with nearby airports
Explanation: Since microwaves are of higher frequency they can have a wide channel from 300 MHz to 300 GHz. This is particularly useful when two airports nearby are aligned equally. The MLS system an all weather guidance system with wide vertical and horizontal beam widths.
11. At what height is the auto flare initiated?
a) 100 ft
b) 50 ft
c) 25 ft
d) 10 ft
Explanation: The auto flare is initiated around 50 ft where the aircraft is over or very near the runway threshold so that the radio altimeter is measuring the height of the aircraft above the runway. Low range radio altimeters are used to ensure accuracy.
12. What type of controller is used in an auto flare control?
a) Proportional plus derivative
b) Proportional plus integral
c) Proportional plus integral plus derivative
d) Proportional only
Explanation: The auto-flare loop is a high-order system; apart from the lags present in the filtered rad.alt. signals there are also the lags present in the response of the pitch attitude command loop. This loop controls and its response is significantly slower at the low speeds during the approach. A proportional plus integral control term is used in the auto-flare controller to ensure accuracy and some phase advance is generally provided to compensate for the lags in the loop and hence improve the loop stability and damping.
13. What is the velocity at the start of flare maneuver if the approach speed is 130 knots?
a) 2.91 m/s
b) 3 m/s
c) 3.56 m/s
d) 10 m/s
Explanation: Vertical velocity at the start of flare = approach speed x glide slope angle. Thus Vv= 66.87* x sin(2.5°) = 2.91 m/s . *[converting knots to m/s].
14. What is the position accuracy that can be achieved by satellite guidance systems?
a) 10 m
b) 5 m
c) 0.5 m
d) 1 m
Explanation: The navigation position accuracy of 1 m which can be achieved with the differential GPS technique is being exploited in the US for landing guidance with a system called the Ground Based Augmentation System, GBAS. The Ground Based Augmentation System, when installed at an airport, will be able to provide the high integrity and accurate guidance necessary for landing in Cat. III visibility conditions.
Sanfoundry Global Education & Learning Series – Avionics.
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