DGCA Air Navigation: Ssr & Tcas Questions
181 exam-style Ssr & Tcas questions for the DGCA Air Navigationpaper (CPL & ATPL). The first 12 are free below with answers and explanations — sign up free to practise all of them with progress tracking.
- Q1
When Mode C is selected on the aircraft SSR transponder the additional information transmitted is:
- A flight level based on 1013.25 hPa
- Baltitude based on regional QNH
- C aircraft height based on sub-scale setting
- Dheight based on QFE
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Correct answer: A. flight level based on 1013.25 hPa
Mode C adds pressure-altitude information referenced to the standard 1013.25 hPa datum, which the ground station converts and displays as the aircraft's flight level.
- Q2
The ground Secondary Surveillance Radar (SSR) equipment incorporates a transmitter and receiver respectively operating in the following frequencies: Transmitter Receiver
- A 1030 MHz 1090 MHz
- B 1090 MHz 1030 MHz
- C 1090 MHz 1090 MHz
- D 1030 MHz 1030 MHz
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Correct answer: A. 1030 MHz 1090 MHz
The ground SSR interrogator transmits on 1030 MHz and listens for the airborne transponder replies on 1090 MHz. The airborne transponder does the reverse, receiving on 1030 and replying on 1090 MHz.
- Q3
Why is a secondary radar display screen free of storm clutter?
- A The principle of 'echo' return is not used in secondary radar
- BThe frequencies employed are too high to give returns from moisture sources
- CA moving target indicator facility suppresses the display of static or near static returns
- DThe frequencies employed are too low to give returns from moisture sources
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Correct answer: A. The principle of 'echo' return is not used in secondary radar
A secondary radar screen is free of weather clutter because it does not rely on reflected echoes; it displays coded replies actively transmitted by the aircraft transponder. With no returned energy from raindrops, precipitation produces no paint.
- Q4
In order to indicate radio failure the aircraft SSR transponder should be selected to code:
- A 7600
- B 7700
- C 7000
- D7500
Show answer
Correct answer: A. 7600
Code 7600 is the SSR transponder setting selected to indicate a radio communications failure. It alerts controllers that the aircraft can no longer transmit or receive.
- Q5
In order to indicate unlawful interference with the planned operation of the flight, the aircraft Secondary Surveillance Radar (SSR) transponder should be selected to:
- A 7500
- B7600
- C 7700
- D 7000
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Correct answer: A. 7500
Code 7500 is the SSR transponder setting used to indicate unlawful interference, i.e. hijacking. Codes 7600 and 7700 signify radio failure and general emergency respectively.
- Q6
When an aircraft is operating its Secondary Surveillance Radar in Mode C an air traffic controller's presentation gives information regarding the aircraft's indicated flight level that is accurate to within:
- A + or - 50 FT
- B + or - 75 FT
- C + or - 100 FT
- D + or - 25 FT
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Correct answer: A. + or - 50 FT
In Mode C the transponder encodes pressure altitude in 100-ft increments, so the flight level shown to the controller is accurate to within ±50 ft of the aircraft's indicated level. This is half of the 100-ft quantising step.
- Q7
The frequency of an SSR ground transmission is:
- A1030 +/- 0.2 Mhz
- B1050 +/- 0.5 Mhz
- C 1090 +/- 0.3 Mhz
- D 1120 +/- 0.6 Mhz
Show answer
Correct answer: A. 1030 +/- 0.2 Mhz
The SSR ground interrogator transmits on 1030 MHz, held to a tolerance of about ±0.2 MHz. The airborne transponder replies on 1090 MHz.
- Q8
The two main design functions of Secondary Surveillance Radar (SSR) Mode S are:
- A air to ground and ground to air data link communications and improved ATC aircraft surveillance capability
- B collision avoidance using TCAS II and improved long range (HF) communication capability.
- Ccontinuous automatic position reporting using Global Positioning System (GPS) satellites and collision avoidance using TCAS II
- D the elimination of ground to air communications and the introduction of automatic separation between aircraft using TCAS II
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Correct answer: A. air to ground and ground to air data link communications and improved ATC aircraft surveillance capability
Mode S was designed to provide selective, discretely addressed interrogation that improves ATC surveillance while also supporting a two-way air-to-ground and ground-to-air data link. It is not a collision-avoidance system in itself, nor does it depend on GPS position reporting.
- Q9
The ATC transponder system,excluding Mode S, contains :
- Atwo modes, each of 4096 codes
- B four modes, each 1024 codes
- C four modes, each 4096 codes
- D two modes, each 1024 codes
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Correct answer: A. two modes, each of 4096 codes
Excluding Mode S, the ATC transponder operates in Mode A and Mode C, and the pulse-position coding scheme provides 4096 possible codes in each of those two modes.
- Q10
A secondary radar can provide up to 4096 different codes.These 4096 codes can be used in:
- A all modes
- B mode A only
- C mode C only
- D mode S
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Correct answer: A. all modes
The 4096 discrete codes are formed by the transponder's pulse-position coding and are available across the operating modes, not restricted to a single mode.
- Q11
The code transmitted by a SSR transponder consists of:
- A pulses
- B phase differences
- C frequency differences
- D amplitude differences
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Correct answer: A. pulses
The SSR transponder replies with a train of coded pulses, the spacing and presence of which convey the identity or altitude code.
- Q12
Which of the following Secondary Surveillance Radar (SSR) codes is used to indicate transponder malfunction?
- A 0
- B7600
- C4096
- D9999
Show answer
Correct answer: B. 7600
Among the standard special-purpose transponder codes, 7600 is set to signify a communication failure. Note that no SSR code specifically denotes a transponder malfunction as such.
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