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Communications and Surveillance

Here, communication and surveillance are the same subject: you know where the aircraft is because it told you, through the same means you use to reply. Losing the means of communication means losing surveillance.

Hierarchy of means

Order Means Function
1 ADS-C Automatic position and route conformance
2 CPDLC Clearances, instructions and reports by text
3 Voice Secondary means, and primary for those without datalink
4 SELCAL Selective calling to recover a silent aircraft

ADS-C and CPDLC are the primary means of the Atlântico ACC, with HF as secondary1.

ADS-C

ADS-C is not radar

The data is dependent and automatic: it comes from the aircraft itself, with the accuracy of its own system, at discrete intervals. There is no independent return, no continuous update, no vectoring. Treating it as a radar screen leads to separation decisions that the data source cannot support.

Contracts established in the Atlântico FIR2:

Type Trigger
Periodic Every 15 minutes
Event Reporting points
Event Lateral deviation of 5 NM
Event Altitude deviation of 200 ft
Event Vertical rate of plus or minus 2,000 ft per minute
Demand Operational need

Event contracts are what turn ADS-C into a conformance tool: any route departure, level deviation or start of climb triggers a notification without you having to ask.

Even under ADS-C, the pilot must send a CPDLC position message on entering the FIR3. Estimates only need to be updated if they change by more than 2 minutes4.

If ADS-C fails, the pilot is normally not alerted by the onboard equipment5. On receiving the failure notification: inform the pilot, require reports by CPDLC or voice and re-establish the applicable minima6.

CPDLC

Logon

The published identifier is SBAO7. Codes for the split sectors are in Structure and sectorization.

Situation Rule
When to log on Between 10 and 25 minutes before entering the FIR8
Departing within the airspace Before take-off8
Coming from a FIR with datalink Automatic transfer; the crew checks it when crossing the boundary9
Logon rejected Callsign and registration must be identical to those in the flight plan10

Rules of use

Rule Source
Whoever speaks by CPDLC gets a CPDLC reply; by voice, a voice reply 11
Every dialogue must be closed 11
A voice clearance prevails over a CPDLC clearance 12
Free text only when no standard message exists; avoid long messages 13
CPDLC is not used for vectoring 14
MONITOR: changes frequency without an initial call 15
CONTACT: changes frequency and makes an initial call 15

If CPDLC fails, revert to voice starting with CPDLC FAILURE, or ALL STATIONS CPDLC FAILURE if the failure is in the ground system. Pending messages are considered not delivered and dialogues start over16. Full phraseology in Phraseology and messages.

Voice

On the network, voice takes place on the position's VHF channel, as per Structure and sectorization. The initial contact needs to establish three things:

  1. Identification: aircraft and unit callsigns.
  2. Situation: position, time, level and, if assigned, speed. The assigned speed is included in the initial call after any frequency change17.
  3. Capability: whether there is an active datalink and whether there is SELCAL.

Real world and simulation

This manual does not claim that VATSIM audio reproduces HF propagation, coverage or degradation. Treat the channel for what it is: a stable voice channel associated with the position.

SELCAL

A four-letter code, mandatory in item 18 preceded by SEL/18. Two practical rules:

  1. Do not perform a SELCAL check on the first contact of an aircraft on CPDLC, unless you request it19.
  2. Use SELCAL to recover an aircraft that does not respond, along with 121.5 MHz, company frequency, air-to-air frequency and other crews20.

Real world and simulation

There is no onboard decoder on the network: the check is a radiotelephony convention. If the pilot does not recognize the procedure, do not insist; agree on a continuous listening watch on the frequency and carry on.

When the primary means fails

Separation cannot depend on a means that no longer exists.

Lost What to do
ADS-C Require reports by CPDLC or voice and re-establish the applicable minima6
CPDLC Revert to voice with CPDLC FAILURE and restart pending dialogues16
Voice Use CPDLC to maintain flight safety until it is restored21
Both Apply the contingencies flow

  1. AIP-Brasil, ENR 3.5, items 8.3.1 and 9.5.1.3. ↩

  2. AIP-Brasil, ENR 3.5, item 9.5.2.3. ↩

  3. AIP-Brasil, ENR 3.5, item 9.5.2.1. ↩

  4. AIP-Brasil, ENR 3.5, item 9.5.2.5. ↩

  5. AIP-Brasil, ENR 3.5, item 9.5.2.6.1. ↩

  6. AIP-Brasil, ENR 3.5, item 9.5.2.6.2. ↩↩

  7. AIP-Brasil, ENR 3.5, item 9.2.1. ↩

  8. AIP-Brasil, ENR 3.5, item 9.2.2. ↩↩

  9. AIP-Brasil, ENR 3.5, item 9.2.3. ↩

  10. AIP-Brasil, ENR 3.5, items 9.2.4 and 9.2.5. ↩

  11. AIP-Brasil, ENR 3.5, item 9.4.1.3. ↩↩

  12. AIP-Brasil, ENR 3.5, item 9.4.1.7. ↩

  13. AIP-Brasil, ENR 3.5, items 9.4.1.1 and 9.4.1.2. ↩

  14. AIP-Brasil, ENR 3.5, item 9.1.6. ↩

  15. AIP-Brasil, ENR 3.5, items 9.4.1.5 and 9.4.1.6. ↩↩

  16. AIP-Brasil, ENR 3.5, items 9.4.4.2 to 9.4.4.5. ↩↩

  17. ICA 100-37, Art. 180. ↩

  18. MCA 100-11, item 2.2.8.1.12, and AIP-Brasil, ENR 3.5, item 9.4.3.2. ↩

  19. AIP-Brasil, ENR 3.5, item 9.5.1.2. ↩

  20. ICA 100-37, Art. 268. ↩

  21. AIP-Brasil, ENR 3.5, item 9.1.4. ↩