Meteorological Aerodrome Reports (METARs) — Page 484, Lesson 457

I want to walk you through how runway surface conditions are reported in a METAR, specifically the friction coefficient or braking action group. This is a critical piece of information for landing performance calculations, especially in winter operations. Let's start with the structure. In the runway state group, the 5th and 6th digits together tell us either the friction coefficient or the braking action. The mean value is transmitted, but if there's a value that is operationally significant—meaning it's the worst one that affects safety—then the lowest value is sent instead. Here's how to read those two digits. If you see "28", that means a friction coefficient of 0.28. "35" means a friction coefficient of 0.35. So the two digits are simply the coefficient expressed as a two-digit number—28 means 0.28, 35 means 0.35, and so on. But there's a separate code for braking action, which uses numbers starting with 91. "91" means braking action: Poor. "92" means Medium/Poor. "93" means Medium. "94" means Medium/Good. "95" means Good. And "99" means the figures are unreliable—for example, if the equipment used doesn't measure satisfactorily in slush or loose snow. If braking action is not reported at all, you'll see two forward slashes: "//". Now, there are several important notes I need to cover. Note 1: If contamination conditions on all runways cease to exist—meaning the runway is no longer contaminated—a special group is sent. It consists of the code "R88/", followed by the abbreviation "CLRD", and then the Braking Action. So you'd see something like "R88/CLRD/93" to indicate the runway is cleared and braking action is Medium. Note 2: Within the UK, friction coefficient measurements are only made on runways contaminated by ice—whether gritted or ungritted—and by dry or compacted snow. If the contamination is caused by water, slush, or wet snow, then the friction coefficient or braking action should be reported as "//"—meaning not reported. Note 3: Runways can only be inspected as frequently as conditions permit. So if a previous half-hourly report is re-issued, it doesn't necessarily mean the runway has been inspected again during that period. It might simply mean that no significant change is apparent. Note 4: This reporting system is completely independent of the normal NOTAM system. These reports are not used by AIS—Aeronautical Information Services—for amending SNOWTAMs received from originators. So you have to treat this as a separate, real-time source of information. If the aerodrome is closed due to contamination of runways, the abbreviation "SNOCLO" is used in place of a runway state group. That tells you the airport is closed because of snow contamination. Now, let's move to Special Reports. A variation on the METAR is the Special Report, denoted by the abbreviation "SPECI". It has the same format as a METAR, except that the code "SPECI" replaces "METAR" at the beginning of the report. A SPECI is issued when the weather conditions significantly change in the period between routine observations. It can indicate either an improvement or a deterioration in the weather. Let me read you an example: "SPECI EGTK 231025Z 26012G25KT 220V300 2000 +RA OVC010 5/M02 Q0991 RETS WS ALL RWY NOSIG". This is a SPECI for EGTK—that's Oxford Airport—issued on the 23rd at 1025 Zulu. The wind is 260 degrees at 12 knots, gusting 25, varying between 220 and 300. Visibility is 2000 metres. There's heavy rain, indicated by "+RA". Overcast cloud at 1000 feet. Temperature 5 degrees, dewpoint minus 2. QNH 0991 hectopascals. "RETS" means recent thunderstorms. "WS ALL RWY" means wind shear on all runways. And "NOSIG" means no significant change expected. So in summary: the 5th and 6th digits of the runway state group give you either the friction coefficient as a two-digit number, or a braking action code from 91 to 95, with 99 for unreliable and "//" for not reported. And a SPECI is just a METAR format report issued between routine observations when conditions change significantly.