Air Information Publications — Page 16, Lesson 22

I want to walk you through the en route navigation aids section of the Air Information Publication — specifically, the UK AIP's ENR 4.1 table. This is the part of the AIP that lists every radio navigation aid available for en route flying, and you'll use it during flight planning to know what navaids are available, on what frequencies, and with what limitations. Let's start with the table structure. The columns are: Name of Station, with the VOR set variation in brackets; IDENT, which is the three-letter morse identifier; Frequency, with the channel number in brackets; Hours of Operation, shown as Winter/Summer; Coordinates in degrees, minutes, and seconds; DME Aerial Elevation; and Remarks. The table gives you everything you need to select and use a navaid. Now let's look at the first entry: Saint Abbs VOR/DME. The VOR set variation is 5.5° West, and that figure is from 1995 — meaning the VOR beacon is physically aligned with magnetic north as it was in 1995. The IDENT is SAB, which in morse code is Sierra Alpha Bravo. The VOR frequency for civil operators is 112.50 MHz, and that same frequency also activates the DME's interrogator and transponder on UHF frequencies. Military aircraft, by contrast, select channel 72X to get range from the DME. The station operates H24 — that's aviation shorthand for 24 hours a day, continuous operation. The coordinates are 55 degrees 54 minutes 27 seconds North, 002 degrees 12 minutes 23 seconds West. The DME antenna sits at 760 feet above mean sea level. Now the remarks are critical: the declared operational coverage, or DOC, is 50 nautical miles and 50,000 feet — but there's an exception. In the sector between 054 degrees magnetic and 144 degrees magnetic, the coverage extends to 200 nautical miles and 50,000 feet. So if you're flying in that sector, you can rely on Saint Abbs much farther out. Next entry: Scotstown Head NDB. The IDENT is SHD, frequency 383.0 kilohertz — notice NDBs are in kHz, not MHz like VORs. Also H24 operation. Coordinates: 57 degrees 33 minutes 33 seconds North, 001 degree 49 minutes 2 seconds West. No DME aerial elevation because an NDB doesn't have DME. The remarks give a standard range of 80 nautical miles, but with a restriction: in the sector from 180 degrees to 335 degrees magnetic, the range drops to just 25 nautical miles. That's a significant limitation you need to know before planning to use that NDB. Third entry: Seaford VOR/DME. Variation 5.5° West from 1997. IDENT SFD. Frequency 117.0 MHz, channel 117X. H24. Coordinates: 50 degrees 45 minutes 38 seconds North, 000 degrees 07 minutes 19 seconds East. DME antenna 300 feet AMSL. The remarks here show a directional coverage pattern: in the sector 260 degrees to 290 degrees magnetic, the DOC is 120 nautical miles and 50,000 feet; elsewhere, it's only 50 nautical miles and 50,000 feet. So Seaford gives you extended coverage only in that specific wedge. Now, the text below the table tells you that exam questions may ask about frequencies and call signs of particular navigation aids. The UK AIP ENR 4 lists them alphabetically, with their morse call signs, transmitting frequencies, operational hours, DME aerial elevation where applicable, and remarks. Then it walks through the Saint Abbs entry in plain language, which I've already covered — but I want to highlight one more point from that explanation: the VOR beacon is aligned with magnetic north, and the variation figure in brackets tells you what year that alignment was set. Also, the DME antenna elevation is given in feet above mean sea level, which matters for line-of-sight calculations. Finally, the last sentence in the excerpt cuts off, but it's telling you the operational limits: neither the VOR nor the DME at Saint Abbs should be used beyond 50 NM and above 50,000 feet, or beyond 200 NM and 50,000 feet in that specific sector. That's your hard limit for flight planning. So to summarise: when you open ENR 4.1 in the UK AIP, you get a table that tells you the station name, its morse identifier, the frequency to select, whether it's H24, its exact position, the DME antenna height, and any directional or altitude restrictions. You need to check the remarks column for every navaid you plan to use, because the standard coverage may not apply in all sectors.