DGCA Air Regulations: ATS Surveillance Services Questions

Correct answer: B. 7600

7600 is the squawk code for RADIO FAILURE. Easy trick: 76 = No talk 76 sounds like seven six — silence). 7500 = Hijacking, 7700 = Emergency. Always squawk 7600 when you lose comms so ATC knows what is happening.

Correct answer: D. 7600

7600 is the squawk code for radio communication failure. Easy memory trick: 76 = no talk. The three emergency codes are: 7700 = General Emergency, 7600 = Radio Failure, 7500 = Hijacking. Remember them as 7-7 emergency), 7-6 no talk), 7-5 hijack).

Correct answer: A. VOR radial

To identify an aircraft on radar, ATC uses the transponder — they ask you to squawk a specific code or press IDENT. They do NOT ask for your VOR radial to identify you on radar. VOR radials are used for navigation position reporting, not radar identification. So ATC does not need your VOR radial to find you on their radar screen.

Correct answer: B. Previously assigned code for first 30 mins, then 2000

The North Atlantic Track system is one of the busiest oceanic routes in the world. When entering NAT airspace, the procedure is: keep your previously ATC-assigned transponder code for the first 30 minutes, then switch to 2000 the standard oceanic squawk code). This 30-minute overlap helps ATC track you smoothly as you transition from radar coverage into oceanic non-radar airspace where 2000 is the standard code used.

Correct answer: A. 7500 – Hijack, 7600 – Communication Failure, 7700 – Emergency/Distress

Every pilot must memorise these three emergency squawk codes: 7500 = Hijack someone is taking over the aircraft illegally), 7600 = Communication failure radio is broken), 7700 = Emergency or Distress any other emergency). A helpful memory trick: 75 — taken alive hijack), 76 — heard nothing radio dead), 77 — going to heaven emergency). These codes instantly alert ATC to your situation without needing radio communication.

Correct answer: A. 7700; 7600; 2000; 7500.

The emergency SSR codes in order are: 7700 = Emergency/Distress any serious emergency), 7600 = Radio Communication Failure radio is broken), 2000 = Entering uncontrolled or specific airspace like the UK without a prior assigned code, 7500 = Unlawful interference hijack). Memory trick: 77 = going to heaven emergency), 76 = heard nothing radio dead), 75 = taken alive hijack), 2000 = entering new airspace.

Correct answer: C. Improved resolution & TCAS

SSR Mode S has two key advantages: 1. IMPROVED RESOLUTION — Mode S can address individual aircraft uniquely 24-bit address), eliminating garbling when two aircraft replies overlap on radar. 2. TCAS — Mode S is the foundation that enables TCAS to work, since aircraft can communicate directly with each other via Mode S data link.

Correct answer: A. Pulse technique

Primary Surveillance Radar works using the PULSE technique. The radar transmits short powerful bursts of radio energy and then listens for the echo. The time between transmitting the pulse and receiving the echo tells the system how far away the target is. It requires NO transponder on the aircraft — it detects the raw reflection from the aircraft's body.

Correct answer: B. 1013.25 hPa

When the aircraft transponder transmits altitude information Mode C) to ATC radar, it ALWAYS uses standard pressure 1013.25 hPa — regardless of what QNH or QFE the pilot has set. This is why ATC sees FLIGHT LEVELS from Mode C, not QNH altitudes. The encoding altimeter is separately referenced to standard pressure, ensuring all aircraft show comparable pressure altitude data.

Correct answer: C. +- 75ft

SSR Mode C transmits the aircraft's pressure altitude to the radar. The accuracy of the displayed altitude data to the Air Traffic Controller is ±75 feet. This is why controllers use Mode C for traffic separation advisories but do not rely on it for precise vertical separation without confirmation.

Correct answer: B. 2.5NM between aircraft on the same localizer course

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Correct answer: C. 5.0NM

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