Avionics MCQs –Microwave Landing System

1 - Question

What is the main weakness of the ILS system?
a) Less power
b) Less range
c) More noise
d) Environment sensitivity
Explanation: The main weakness of the ILS system was its sensitivity towards the environmental factors. Since the frequency used by the system is in MHz, it was more susceptible to atmospheric and weather interference.

2 - Question

What does the MLS use to overcome the weakness of ILS system?
a) Narrow beam width antennas
b) More power
c) Filers for separating noise
d) Array of antennas
Explanation: The main weakness of the ILS system is eliminated by using narrow beam width antennas which are physically small since the frequency is high. As frequency increases antenna size decreases.

3 - Question

Which of the following is not one of the basic components of the MLS system?
a) Azimuth ground station
b) Elevation ground station
c) DME
Explanation: A basic MLS consists of azimuth and elevation ground stations and a conventional DME for 3D positioning on approach course to 40° on either side of center line and to 15° elevation above the runway.

4 - Question

Why is a back azimuth station used in some MLS?
a) Better range
b) Less noise
c) Missed approach
d) Back up for main azimuth station
Explanation: An expanded MLS system uses back azimuth stations. It is generally used for departure and for missed approaches. It provides lateral guidance to 40° on either side of the center line.

5 - Question

What is the number of channels in the MLS system?
a) 10
b) 50
c) 4000
d) 200
Explanation: The MLS station transmit both angle and data functions on one of 200 frequencies between 5031.0 and 5190.7 MHz. The relatively high number of channels allows the use of multiple MLS in metropolitan cities.

6 - Question

Which of the following determines the required transmission power in MLS?
a) Noise
b) Bit error rate
c) Runway length
d) Aircraft size
Explanation: The acceptable bit error rate of the differential phase shift keying (DPSK) transmissions at the 20-nmi limit determines the transmitter power needed in the ground stations.

7 - Question

Using an audio tone to encode angles is an efficient method.
a) True
b) False
Explanation: Early MLS with mechanical scanned array used a varying audio tone to encode the pointing angle on the scanning beam pattern. The FAA adopted the time interval between successive passages of the unmodulated beam as an efficient means of angle encoding.

8 - Question

What is the typical scanning rate of the MLS antenna?
a) 20,000°/sec
b) 10000°/sec
c) 500°/sec
d) 37°/sec