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6/17/21 

Pilot/Controller Glossary 

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.) 

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. 

PCG B