Airports with special braking measuring equipment, such as the Runway Friction Meter (also known as the Mu Meter) report the runway conditions as a measurable quantity. Without such equipment (as with the majority of airports in the world) breaking action conditions are rated and reported by pilots.
The four official terms for reporting breaking action are: good, fair, poor, and nil. Of course, one pilot may use poor when another pilot describes the same conditions as fair - this is an unavoidable result of non-quantitative assessment. However, the terms good and nil are easier to define. Breaking action good indicates the runway conditions are unaffected by the freezing precipitation - conditions like those following rain or when the runway is completely dry. Most airports with effective snow and ice removal equipment can maintain good breaking action conditions during a storm or achieve this level soon after.
Nil breaking action indicates no breaking action at all. This level is used for the worst icing conditions possible. When breaking action is determined to be nil, the runway is closed for routine operations and only emergencies should be allowed to land. Basically, and aircraft’s brakes are ineffective in these conditions and only flaps and/or reverse thrust can be used to slow an aircraft. Another important detail about breaking action conditions is that the report must contain the type of aircraft which reported them. Breaking action conditions to a Cessna 150 may be interpreted differently from a Gulfstream 550. The following is a standard dialogue between ATC and a Citation 550 landing after a winter storm.
N550MH: “Tower, Citation 550MH, with you final approach fix ILS Runway 5 request full stop.”
ATC: “Citation 550MH, Tower, Runway 5 cleared to land, patchy snow (3) on runway breaking action reported good by a Lear 23.”
N550MH: “Tower, Citation 550MH copies cleared to land breaking action good.”
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