Braking action is something most pilots rarely need to think about. But when water, ice, snow, oil, or other contaminants get onto a runway, the effectiveness of aircraft brakes can be severely impaired, making it difficult or impossible to stop. Braking action is described in four ways - good, fair, poor, or nil. When tower controllers have received runway braking action reports from pilots that include the terms poor or nil, they will issue a braking action advisory and the ATIS broadcast will include the words, "Braking action advisories are in effect." Such advisories also are issued when weather conditions are conducive to rapidly changing or deteriorating braking conditions. While the advisories remain in effect, controllers will give each landing and departing aircraft the latest braking action report. Pilots should ask for the information if controllers do not volunteer it. Pilots who are landing at an airport with an active braking action advisory should also be prepared to describe their experience to controllers using the terms good, fair, poor, or nil.