SELCAL stands for Selective Calling — Page 138, Lesson 213

I want to walk you through the SELCAL procedures and position reporting requirements for the North Atlantic region. Let's start with SELCAL. SELCAL stands for Selective Calling. It's a system that allows air traffic control to call a specific aircraft over HF radio without the pilot having to listen to all the background noise and chatter on the frequency. When you're flying across the ocean, HF communications can be noisy, and SELCAL lets the system alert you only when ATC is trying to reach your aircraft specifically. Now, even when you're using HF communications, and even when you're using ADS-C (Automatic Dependent Surveillance – Contract) or CPDLC (Controller Pilot Data Link Communications), you as a pilot must still maintain a listening watch on the assigned frequency. However, if your aircraft is fitted with SELCAL, you have a different set of responsibilities. Instead of just listening continuously, you must follow a specific sequence of actions. First, you must provide the SELCAL code in the flight plan. That four-letter code tells ATC how to address your aircraft. If the aircraft changes for a subsequent flight — say you swap planes — you must pass the new SELCAL information to the OAC, which is the Oceanic Area Control centre. Second, you must check the operation of the SELCAL equipment at or prior to entry into oceanic airspace. You do this with the appropriate aeradio station. This SELCAL check must be completed before you commence SELCAL watch. In other words, you verify the system works before you start relying on it. Third, after that check, you maintain a SELCAL watch. That means your SELCAL receiver is active and listening for your code, and you are monitoring for the alert. Here's a critical point: even if you are using SATCOM Voice (satellite communications voice) or ADS/CPDLC for routine air/ground ATS communications, you must still comply with these SELCAL provisions. Why? Because it ensures that ATC always has a timely means of contacting your aircraft. If one system fails, they can still reach you through SELCAL. Now let's move to Position Reports. The air traffic control system used across the NAT region — the North Atlantic — is procedural ATC. This is different from radar-based control. Procedural ATC relies entirely on pilot position reports to confirm separation between aircraft. There is no radar coverage over the ocean, so ATC depends on you telling them where you are. The routes are organized so that east/west routes cross whole 5 degrees of longitude at whole degrees of latitude. Similarly, north/south routes cross whole 10 degrees of latitude at whole degrees of longitude. At these crossing points, pilots are required to make position reports. For an east/west route, that works out to approximately every 500 nautical miles. This meets the ICAO requirement that position reports be made at intervals not greater than 1 hour. Standard air/ground message types and formats are used within the NAT Region. These are published in State AIPs (Aeronautical Information Publications) and Atlantic Orientation charts. To help ground stations process messages as quickly as possible, you must observe four rules. First, use the correct type of message for the data you are transmitting. Second, state the message type in the contact call to the ground station, or at the very start of the message. Third, adhere strictly to the sequence of information for that type of message. Fourth, all times in any message must be expressed in hours and minutes UTC — Coordinated Universal Time. Let me give you the two main message types with examples. A Position report sounds like this: "Position, Swissair 100, on 8831, RESNO at 1235, Flight Level 330, Estimating 56 North 020 West at 1310, 56 North 030 West Next." You state the word "Position," your callsign, the frequency you're on, the fix you're over and the time, your current flight level, your next estimated position and time, and the following fix. A Request Clearance message looks like this: "Request Clearance, American 123, on 8831, 56 North 020 West at 1308, Flight Level 330, Estimating 56 North 030 West at 1340, 56 North 040 West Next. Request Flight Level 350." You start with "Request Clearance," then your callsign, frequency, your current position and time, flight level, your estimate for the next fix, and the fix after that, then state what you're requesting. If a position report is not required at that moment, you can simplify it: "Request Clearance, Speedbird 212 on 3476, Request Flight Level 370." Just the callsign, frequency, and your request.