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. 

## BASE LEG- 

(See TRAFFIC PATTERN.) 

## BEACON- 

(See AERONAUTICAL BEACON.) (See AIRPORT ROTATING BEACON.) (See AIRWAY BEACON.) (See MARKER BEACON.) (See NONDIRECTIONAL BEACON.) (See RADAR.) 

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. 

## BLIND TRANSMISSION- 

(See TRANSMITTING IN THE BLIND.) 

## B 

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- 

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- 

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. 

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. 

(See BLIND SPOT.) 

(See AIRPORT LIGHTING.) 

(See RUNWAY CONDITION READING.) (See RUNWAY CONDITION REPORT.) (See RUNWAY CONDITION CODES.) 

