SVFR stands for Special Visual Flight Rules — Page 126, Lesson 202

Let's pick up with the special VFR procedure, because ICAO adopted it as an international standard. SVFR stands for Special Visual Flight Rules. ICAO defines it as a VFR flight cleared by ATC to operate within a CTR — that's a Control Zone — in meteorological conditions below VMC, which is Visual Meteorological Conditions. So normally, VFR requires you to stay in VMC, but SVFR is the exception that lets you fly in worse weather, but only inside a CTR. Now, the key restriction: SVFR is only applicable to flights into, out of, or within a CTR. So you can't use it anywhere else. And ICAO sets a hard minimum: the ground visibility within the CTR must not be less than 1500 metres before a SVFR flight is permitted to enter the CTR to land, take off and depart, cross, or operate locally within the CTR. So that's the ICAO baseline — 1500 metres. But here's where it gets more restrictive. JAR OPS-1, which is the European operating rules, requires 3000 metres visibility for a SVFR flight to be commenced. So if you're starting a SVFR flight under JAR OPS-1, you need double the visibility — 3000 metres, not 1500. That's a critical distinction for your exams: ICAO says 1500, JAR OPS-1 says 3000 for commencement. Now let's move to distress and urgency signals, because these are defined precisely and you must know them cold. First, distress. The definition: an aircraft, or vessel, is in grave and imminent danger and requests immediate assistance. The distress message is preceded by the word MAYDAY, repeated three times. So you say "MAYDAY, MAYDAY, MAYDAY." And there are visual signals from an aircraft in distress. These may include a succession of red pyrotechnics, or a red parachute flare. So red is the distress colour — red pyrotechnics in succession, or a red parachute flare. Next, urgency. The definition: an aircraft has an urgent message to transmit concerning the safety of a ship, aircraft, vehicle, or other property of a person on board or within sight. So it's not that you're in immediate danger yourself — it's that you have an urgent message about safety of someone or something else. The urgency message is preceded by the words PAN PAN, repeated three times. So "PAN PAN, PAN PAN, PAN PAN." Then there's the non-emergency situation. This is a specific case: if an aircraft has a communications failure or a malfunction that makes it imperative that the aircraft is landed, but the pilot does not require any other assistance — so you can land yourself, you just need to get down — then the pilot shall indicate the fact by repeatedly switching the landing lights, or any other light, on and off. So that's the visual signal for "I have a problem, I need to land, but I don't need help." Finally, SSR — Secondary Surveillance Radar. That's covered in depth in Chapter 13 and in Radio Navigation, but there are certain reserved codes, called squawks, that have specific meaning, and you're required to know them. At all times, you should transmit the altimeter function — that's Mode Charlie — in addition to the reserved codes. So Mode Charlie gives your altitude, and you always transmit that alongside the reserved code. The reserved transponder codes are three. Mode A code 7700 — this is the civil emergency code. It's used unless a specific identification code has been allocated by a radar controller and the aircraft has been identified. So if you're not already identified, 7700 is your emergency squawk. Mode A code 7600 — this is the squawk to indicate radio failure. It should be used at all times when a failure occurs, regardless of the ATC service being provided. So whether you're talking to anyone or not, if your radio fails, you squawk 7600. And Mode A code 7500 — this code indicates unlawful interference. Its use does not imply that the fact is being generally advertised. So 7500 means you're being hijacked or interfered with, but you don't broadcast that openly — the code itself is the silent signal. So to recap the three: 7700 emergency, 7600 radio failure, 7500 unlawful interference. And always with Mode Charlie altitude reporting on top.