Control of Aircraft — Page 333, Lesson 433

Let's get into radar separation and radar identification. This is the heart of how an air traffic controller actually uses radar to keep aircraft apart and to help you. First, the separation standard. There is only one radar separation standard, and that is 5 nautical miles. That's the baseline. Now, as we covered in Chapter 16, reduced radar separation may be applied under specific conditions, but the standard is 5 NM. And here's a key point: the separation applied is based upon the aircraft position derived from PSR only. PSR is Primary Surveillance Radar — that's the radar that works by bouncing a signal off the aircraft's skin, so it's independent of anything the aircraft transmits. So the 5 NM separation is based on where the aircraft actually is as seen by that primary radar return. Now, wake turbulence separation — that's the separation needed to keep you out of the vortices left behind by a preceding aircraft. As defined in Chapter 16, wake turbulence separation can be applied using radar-derived information. In that case, the separation standards applied are based on distance, not on time. So when the controller is using radar to apply wake turbulence separation, they're measuring distance between the aircraft. Now, before a radar controller can provide any service to an aircraft, the radar identity of the aircraft must be established. This is the requirement. The controller has to know which blip on the screen is you. The most common method is SSR — Secondary Surveillance Radar. The basic SSR capability is to identify a specific aircraft squawking a specifically allocated code. So the controller allocates you a code, you squawk it, and that identifies you. It's the most commonly used method and it's also the quickest. Once an aircraft has been allocated an SSR code, it must be retained until otherwise advised by the radar controller. So you keep that code until the controller tells you to change it. And here's an important point for you as a pilot: if an emergency situation arises, the pilot should not squawk A7700 if the identity of the aircraft has already been established using SSR. A7700 is the emergency code, but if you're already identified by your allocated code, you don't change to A7700 — you keep your allocated code so the controller doesn't lose your identity. Now, all other methods of identification by radar require the ATCO — the Air Traffic Control Officer — to observe the radar contacts on the display screen and determine, either from geographic position or from a specific manoeuvre, which contact is the aircraft requiring the service. Let me walk you through those methods. Geographic location — for example, "2 NM west of Woodstock." The controller knows where you are relative to a known point. Relative to a radio navigation aid — for example, "On the 230 radial from the Daventry VOR DME 5 NM." So you're on a specific radial from a VOR, at a specific DME distance. Latitude and longitude — the controller can use your reported position in lat/long. Georef position — that's a military grid reference system, a way of giving a position on a map. Turn through 30° or more away from desired course and then return to the course — this is a manoeuvre the controller asks you to do. You turn at least 30 degrees off your course and then come back, and the controller watches your blip make that distinctive turn to confirm it's you. And finally, positive handover from a radar controller who had previously identified the aircraft. So if one controller has already identified you, they can hand you over to another controller who can accept that identification. Now, the procedure. When identifying a radar contact as a specific aircraft, the radar controller must tell the pilot how the identification was achieved. So the controller will use the phrase "radar contact" to indicate that the aircraft has been identified and that until further advised, a service will be provided. For example: "G-CD radar contact 2 NM west of Oxford." That position should agree with the position the pilot thinks the aircraft is at. If it's significantly different, the pilot must inform the controller — because the controller might have misidentified the aircraft. So you, as the pilot, have a duty to speak up if the position given doesn't match where you think you are. Now, the radar service itself. Commencement: after identification, the pilot is to be told what type of radar service is to be provided and what the objective is. For example: "G-CD radar contact 6 NM west of Compton, radar control, expect radar vectors for ILS approach runway 26." So you're told it's radar control, and the objective is radar vectors for an ILS approach — that's the Instrument Landing System — on runway 26. Termination: when an aircraft reaches the limit of radar cover, or the edge of a radar vectoring area, or the aim of the service has been achieved, the pilot will be advised that the service is terminated. The controller gives you position information and instructions or advice on how to continue. For example: "G-CD radar service terminated, presently 10 NM south of Benson, resume own navigation, suggest continue with London Information 125.650." So you're told the service is over, where you are, to resume your own navigation, and a suggested frequency to continue with. Let me just tie that together. The key flow is: identify you, tell you how you were identified, tell you what service you're getting and why, then when it's done, tell you it's terminated and give you position and how to continue. And throughout, the separation standard is 5 NM based on PSR position, with wake turbulence separation based on distance when radar-derived information is used.