Pilot/Controller Glossary  8/15/19  B  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.  (See NONDIRECTIONAL BEACON.)  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.  BLAST PAD- A surface adjacent to the ends of a  runway provided to reduce the erosive effect of jet  blast and propeller wash.  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.  (See ICAO term BLIND VELOCITY.)  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.  (See TRANSMITTING IN THE BLIND.)  BLIND TRANSMISSION- 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.  BLIND ZONE- (See BLIND SPOT.)  BLOCKED- Phraseology used to indicate that a  radio transmission has been distorted or interrupted  due to multiple simultaneous radio transmissions.  BOTTOM ALTITUDE– In reference to published  altitude restrictions on a STAR or STAR runway  transition, the lowest altitude authorized.  BOUNDARY LIGHTS- (See AIRPORT LIGHTING.)  BRAKING ACTION (GOOD, GOOD TO MEDI- UM, MEDIUM, MEDIUM TO POOR, POOR, OR  NIL)- A report of conditions on the airport  movement area providing a pilot with a degree/quali- ty of braking to expect. Braking action is reported in  terms of good, good to medium, medium, medium to  poor, poor, or nil.  (See RUNWAY CONDITION READING.)  (See RUNWAY CONDITION REPORT.)  (See RUNWAY CONDITION CODES.)  BRAKING ACTION ADVISORIES- When tower  controllers receive runway braking action reports  which include the terms “medium," “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 most  current 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 issued 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 simultaneous  (independent) parallel operations, a breakout is used  to direct threatened aircraft away from a deviating  aircraft.  BASE LEG- BEACON- (See TRAFFIC PATTERN.)  (See AERONAUTICAL BEACON.)  (See AIRPORT ROTATING BEACON.)  (See AIRWAY BEACON.)  (See MARKER BEACON.)  (See NONDIRECTIONAL BEACON.)  (See RADAR.)  PCG B-1 