Use of ATS Surveillance Systems
Air Regulations · Chapter 8 · DGCA CPL and ATPL
How radar and its cousins find you, prove which blip is you, and how close they then let aircraft fly.
Remember
- Surveillance separation is 5 NM as standard, 3 NM where allowed, and 2.5 NM on the same final within 10 NM of the threshold.
- Below 10,000 ft the speed limit is 250 kt IAS; arrivals within 15 NM of the VOR/DME are held to 220 kt IAS.
- Mode C must agree with your reported level within 200 ft in RVSM airspace and 300 ft elsewhere.
- With primary radar only, identification by turn needs one or more turns of 30° or more.
- Squawk 7500 hijack, 7600 radio failure, 7700 emergency, 2000 when no code is assigned.
What does surveillance let ATC do?
The big picture
See it, prove which blip it is, then space it out. Tap + to open.
- ATS surveillance see, identify, separate ATC uses surveillance systems that let it see and identify aircraft, and then separate and control them.
- See the aircraft five systems Aircraft can be seen by primary radar, secondary radar, ADS-B, ADS-C or multilateration, and shown as symbols, PSR blips or SSR responses.
- Primary radar (PSR) echo off the airframe Needs nothing in the aircraft, so it is the only one that sees traffic without a transponder.
- Secondary radar (SSR) ground asks, aircraft replies Needs a Mode A, C or S transponder. Gives identity and pressure altitude.
- ADS-B and ADS-C aircraft reports its position ADS-B broadcasts to everyone; ADS-C reports point-to-point by contract, used in oceanic and remote areas.
- Multilateration (MLAT) times replies at several receivers Works with a standard transponder. Used on the airport surface and in terminal areas.
- Identify it before any service Before any ATS surveillance service is given, the aircraft must be identified and the pilot told; if identification is lost, the pilot is told that too.
- ADS-B 3 ways With ADS-B, an aircraft is identified by its ID in the ADS-B label, by transfer of identification, or by its response to TRANSMIT ADS-B IDENT.
- Recognise the ID in the label The controller directly recognises the aircraft identification shown in its ADS-B label.
- IDENT feature The pilot is told to TRANSMIT ADS-B IDENT and the controller watches for that response.
- Transfer from another controller ADS-B identification is handed over from another controller.
- SSR or MLAT 4 ways With SSR or MLAT, identification uses the ID in the label, a verified discrete code, a Mode S aircraft ID, transfer, setting a code, or squawk IDENT.
- Discrete code The controller recognises an assigned discrete code, whose setting has been verified, in the SSR or MLAT label.
- Squawk IDENT The pilot is told to squawk IDENT and the controller watches for that response.
- Mode S aircraft ID in the label A Mode S aircraft's callsign shows up by itself in its SSR or MLAT label, so the controller recognises it directly.
- Transfer from another controller Identification is handed over from another controller.
- Primary radar only 3 ways With primary radar alone, the aircraft is identified by the position report method, the departing aircraft method or the turn method.
- Your reported position Matched with a target at that bearing and distance.
- Departing target within 1 NM of the runway end A target seen just after take-off is matched with the aircraft known to have departed, if identification is made within 1 NM of the runway end.
- One or more turns of 30° or more The controller checks that only one target follows the turn, then says 'Radar identified'.
- ADS-B 3 ways With ADS-B, an aircraft is identified by its ID in the ADS-B label, by transfer of identification, or by its response to TRANSMIT ADS-B IDENT.
- Separate and control spacing, speed, vectors Identified aircraft are kept apart by surveillance minima, speed control and radar vectors.
- 5 NM standard 3 NM where allowed 2.5 NM between aircraft on the same final approach track, inside 10 NM of the threshold.
- Speed control 250 kt, 220 kt within 15 NM Below 10,000 ft: 250 kt IAS for all aircraft; arrivals within 15 NM of the VOR/DME 220 kt IAS.
- Vectors magnetic headings only Radar vectors are always given as magnetic headings.
- Service ends on 'contact tower' Radar service ends automatically when an arrival is told to contact tower. The range from touchdown is given first.
- Transponder rules Indian FIRs In the Indian FIRs the transponder is operated throughout flight, kept off on the ground except on the runway, and set to the assigned code or 2000.
- On at all times in flight Chennai, Delhi, Guwahati, Kolkata and Mumbai FIRs.
- Off on the ground until entering the runway Turned off again after fully vacating the runway on landing.
- 2000 if no code assigned An aircraft with no SSR code assigned squawks Mode A code 2000 before entering the Indian FIRs and keeps it until told otherwise.
- 7500, 7600, 7700 emergency codes Unlawful interference, radio failure, general emergency.
- See the aircraft five systems Aircraft can be seen by primary radar, secondary radar, ADS-B, ADS-C or multilateration, and shown as symbols, PSR blips or SSR responses.
Memory hook: See, identify, separate.
Takeaway: Only primary radar sees an aircraft with no transponder. Identification comes first; separation and speed control follow.
What is surveillance used for?
What it's for
Purposes, where it's used and the three services. Tap + to open each.
This lesson is part of the Exam-Ready plan. See plans
ADS-B, ADS-C and MLAT: what's the difference?
ADS-B, ADS-C, MLAT
Same idea, different delivery. Read across.
This lesson is part of the Exam-Ready plan. See plans
How does primary radar alone pick you out?
Primary radar ID
No transponder label to read, so the controller watches the blip move.
Memory hook: Thirty or more: not 10, not 45.
Takeaway: A turn of 30° or more that only one target follows, or a target within 1 NM of the runway end after take-off.
Which system uses this identification method?
Which ID method?
Tap a method, then the system it belongs to.
This lesson is part of the Exam-Ready plan. See plans
How close can surveillance bring two aircraft?
Separation
Three minima, drawn to the same scale. The closer to the runway, the closer the spacing.
This lesson is part of the Core plan. See plans
How fast may you fly near the aerodrome?
Speed limits
Two limits below 10,000 ft. The tighter one applies to arrivals close to the VOR/DME.
This lesson is part of the Core plan. See plans
Transponder or radar fails: what now?
Something fails
Answer about what has failed.
This lesson is part of the Exam-Ready plan. See plans
How does ATC check the level your transponder shows?
Level check
From your first call to the moment the controller stops using a bad readout.
This lesson is part of the Core plan. See plans
Which code should your transponder show?
Which squawk
Read each case and press the stamp that applies.
This lesson is part of the Core plan. See plans
Which code, how accurate, and how close on radar?
Codes and gaps
Four views: squawk codes, the Mode C check, surveillance spacing and India's rules.
This lesson is part of the Exam-Ready plan. See plans
Numbers to know
Numbers
The figures examiners like, in one list.
This lesson is part of the Core plan. See plans
Pairs that catch students out
Don't mix up
Five pairs that look alike in the exam.
This lesson is part of the Core plan. See plans
Test yourself
Ten questions from this chapter.
This lesson is part of the Core plan. See plans