BACK-TAXI- A term used by air traffic controllers to taxi an aircraft on the runway opposite to the traffic flow. The aircraft may be instructed to back-taxi to the beginning of the runway or at some point before reaching the runway end for the purpose of departure or to exit the runway.
BEARING- The horizontal direction to or from any point, usually measured clockwise from true north, magnetic north, or some other reference point through 360 degrees.
BELOW MINIMUMS- Weather conditions below the minimums prescribed by regulation for the particular action involved; e.g., landing minimums, takeoff minimums.
BLAST FENCE- A barrier that is used to divert or dissipate jet or propeller blast.
BLIND SPEED- The rate of departure or closing of a target relative to the radar antenna at which cancellation of the primary radar target by moving target indicator (MTI) circuits in the radar equipment causes a reduction or complete loss of signal.
BLIND SPOT- An area from which radio transmissions and/or radar echoes cannot be received. The term is also used to describe portions of the airport not visible from the control tower.
BLIND VELOCITY [ICAO]- The radial velocity of a moving target such that the target is not seen on primary radars fitted with certain forms of fixed echo suppression.
BLOCKED- Phraseology used to indicate that a radio transmission has been distorted or interrupted due to multiple simultaneous radio transmissions.
BRAKING ACTION (GOOD, FAIR, POOR, OR NIL)- A report of conditions on the airport movement area providing a pilot with a degree/quality of braking that he/she might expect. Braking action is reported in terms of good, fair, poor, or nil.
BRAKING ACTION ADVISORIES- When tower controllers have received runway braking action reports which include the terms "poor" or "nil," or whenever weather conditions are conducive to deteriorating or rapidly changing runway braking conditions, the tower will include on the ATIS broadcast the statement, "BRAKING ACTION ADVISORIES ARE IN EFFECT." During the time Braking Action Advisories are in effect, ATC will issue the latest braking action report for the runway in use to each arriving and departing aircraft. Pilots should be prepared for deteriorating braking conditions and should request current runway condition information if not volunteered by controllers. Pilots should also be prepared to provide a descriptive runway condition report to controllers after landing.
BREAKOUT- A technique to direct aircraft out of the approach stream. In the context of close parallel operations, a breakout is used to direct threatened aircraft away from a deviating aircraft.
BROADCAST- Transmission of information for which an acknowledgement is not expected.
BROADCAST [ICAO]- A transmission of information relating to air navigation that is not addressed to a specific station or stations.