Avionics MCQs –Modes S System

1 - Question

How does mode S system differ from mode A and C?
a) Extension of secondary radar
b) Uses pulse technology
c) More data can be transferred
d) One way travel of radio signal
View Answer Answer: c
Explanation: The mode S system works similar to that of mode A and mode C system and causes a transponder to reply when its identity is not known. In a mode S system, additional data other than just altitude and identity can be provided in the MTI.

2 - Question

What is the frequency of interrogation pulse in secondary radar?
a) 1020 MHz
b) 1300 MHz
c) 1030 MHz
d) 1500 MHz
View Answer Answer: c
Explanation: The interrogation pulse is transmitted at 1030 MHz and the reply pulse by the aircraft transponder is given at 1090 MHz. Since the reply is coded information, it does not interfere with other transponders that are using the same frequency.

3 - Question

Which mode is used for selective calling?
a) Mode A
b) Mode B
c) Mode C
d) Mode S
View Answer Answer: d
Explanation: Different modes have its own unique features; mode A gives only identity, mode c gives identity and altitude, mode B is used in European operations and mode S is used for selective calling of transponders.

4 - Question

What are the numbers of non-selective interrogations in mode S system?
a) 5
b) 6
c) 7
d) 8
View Answer Answer: b
Explanation: Mode S interrogations are divided into two types: selective and non-selective. The non-selective are the simplest and include familiar techniques. There is a total of 6 non-selective interrogations.

5 - Question

How does mode S identify each aircraft?
a) Unique code for each transponder
b) Lapsed time
c) RCS
d) Directly talking to the pilot
View Answer Answer: a
Explanation: Unlike the ATCRBS where a squawk code is dialed into the transponder, a mode S transponder has a unique identity permanently assigned to it. The mode S radar system can have more than 16 million different identities, enough for each airplane in the world to have a unique identity.

6 - Question

The error caused by two aircraft flying close to each other replying to the same interrogation pulse is called ______
a) Garble
b) Fruit
c) Noise
d) Interference
View Answer Answer: a
Explanation: If several aircraft are within the range of the secondary radar and reply to the same interrogation pulse there is a chance that two reply pulses can overlap each other and cause an error in the values of interfere with different aircraft.

7 - Question

Transmission of modes reply at regular interval to aid TACS is called ________
a) Garble
b) Squitter
c) Fruit
d) Pulsed Radar
View Answer Answer: b
Explanation: An important transponder characteristic that aids TCAS is the transmission of a mode S reply at quasi-random intervals of about 1 sec, which is called squitter.

8 - Question

A mode S transponder is silent when it is not interrogated.
a) True
b) False
View Answer Answer: b
Explanation: Usually, a transponder remains silent when not interrogated. However, being an integral part of TCAS requires the occasional spontaneous mode S transmissions.

9 - Question

Both ATCRBS and mode S have the same range.
a) True
b) False
View Answer Answer: a
Explanation: Mode S system and ATCRBS have the same interrogation frequency and the same reply frequency. The transmitter power output is similar to the ATCRBS transponder as is the receiver sensitivity which ensures that mode S transponders will have similar service ranges as ATCRBS transponders.

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