Airways — Page 158, Lesson 160

I want to walk you through the structure of Air Traffic Services routes, or ATS routes, as they appear in the UK AIP. This is a new topic, so let’s start from the ground up. First, the examination will also test you on Approach Charts, just like it does on SIDs and STARs. The legend for these charts is comprehensive, and you need to be very familiar with its layout and content. The subdivisions that are potential sources of exam questions include: Landing Minimums, Airport Chart Format and Plan View, Additional Runway Information, Lighting Systems, Take-off and Alternate Minimums, GPS Approach Charts, and ICAO recommended airport signs and runway markings. Keep those categories in mind. Now, onto the main subject: ATS Routes. In the United Kingdom, these routes are based on significant geographical points. Those points may or may not coincide with the location of a radio navigation aid. You can find these significant points listed in column 1 of the table at ENR 3 of the UK AIP. Let’s define the standard width of an airway. Unless stated otherwise, an airway is 5 nautical miles either side of a straight line joining each two consecutive points shown in column 1 of that table. So the total width is 10 nautical miles. For Upper ATS routes and Advisory Routes, there is no declared width, but for the purposes of ATS provision, they are also deemed to be 5 NM either side of that straight line. The vertical extent of any route is shown in column 3 of the table. ENR 3 is divided into several categories. Let’s go through them one by one. First, Lower ATS Routes. These have an upper limit of Flight Level 245, or FL245. A reference example is given: see B1 ATS route, defined by the 279 and 085 radials from WAL VOR/DME at position N5323.5 W00308.0. Second, Lower ATS Routes – ATS Advisory Routes. These have a maximum upper limit of FL240, one flight level lower than standard Lower ATS Routes. The route designator for an Advisory Route always ends with the letter D. For example, A1D or N562D. A reference example is W911D Advisory Route, defined by the 242 and 058 radials from IOM VOR/DME at N5404.0 W00445.7. Now, a critical note: Advisory Routes are class F airspace. That means they are not established within Controlled Airspace. They are designated routes along which an Air Traffic Advisory Service is available. What is an Air Traffic Advisory Service? It is a service provided within advisory airspace to ensure separation, in so far as is practical, between aircraft which are operating on IFR flight plans. So it’s a less complete service than full Air Traffic Control. That brings us to the definition of Controlled Airspace. Controlled Airspace is airspace of defined dimensions within which an Air Traffic Control Service is provided to IFR and VFR flights, in accordance with the airspace classification – that’s classes A, B, C, D, and E. An Air Traffic Control Service provides a much more complete service than an Advisory Service. Its responsibilities are: - Preventing collisions between aircraft. - Preventing collisions on the manoeuvring area between aircraft and obstructions. - Expediting and maintaining an orderly flow of air traffic. Third, Lower ATS Routes – Conditional Routes (CDR). These routes are usable only under specified conditions. You would refer to ENR 1.1.1.1 paragraph 1.5 and ENR 3.2.2.1 for those conditions. Fourth, Upper ATS Routes. These extend from FL245 up to FL460. The route designator is always preceded by the letter U. For example, UA1 or UB40. A reference example is UG1 Upper ATS route, defined by the 295 and 111 radials from STU VOR/DME at N5159.7 W00502.3. Finally, there are also Upper ATS Routes – Conditional Routes (CDR), which follow the same conditional-use principle as the lower ones. So, to summarise the key distinctions: Lower routes go up to FL245, Upper routes go from FL245 to FL460. Advisory Routes have a D suffix, are class F, and top out at FL240. Conditional Routes are only usable under specific conditions. And the fundamental difference between an Air Traffic Advisory Service and an Air Traffic Control Service is that Control provides positive separation and collision prevention, while Advisory provides separation only in so far as is practical for IFR aircraft on flight plans.