BACK COURSE (BC)
The reciprocal of the localizer course for an ILS. When flying a back-course approach, an aircraft approaches the instrument runway from the end at which the localizer antennas are installed.

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.

BAILOUT BOTTLE
Small oxygen cylinder connected to the oxygen mask supplying several minutes of oxygen. It can be used in case of primary oxygen system failure or if an emergency bailout at high altitude became necessary.

BALANCE TAB
An auxiliary control mounted on a primary control surface, which automatically moves in the direction opposite the primary control to provide an aerodynamic assist in the movement of the control. Sometimes referred to as a servo tab.

BALLAST
Gas ballooning term; used to control buoyancy, and therefore altitude, during flight. Ballast, usually in the form of sand or water, is carried aloft by the gas balloon at launch. As the balloon pilot needs to adjust altitude, a small amount of ballast is jettisoned overboard, thereby reducing the gross weight of the balloon at that point in time. The balloon will then rise to a new pressure altitude, where it will remain until there is another dynamic change in the lift equation.

BALLISTIC PARACHUTE SYSTEM (BPS)
An optional parachute system activated by the pilot where the parachute is extracted for the WSC by a rocket.

BALLOON
A lighter-than-air aircraft that is not engine driven, and that sustains flight through the use of either gas buoyancy or an airborne heater.

BALLOON AIRCRAFT
The result of a roundout (flare) that is too aggressive during landing, causing the aircraft to climb.

BALLOON FEDERATION OF AMERICA (BFA)
A national association for balloon pilots and enthusiasts in the United States, and affiliated with the National Aeronautic Association. Information about the BFA can be found at www.bfa.net

BALLOON FLIGHT MANUAL
A manual containing operating instructions, limitations, weight, and performance information, which must be available in an aircraft during flight. Portions of the flight manual are FAA approved.

BANK ATTITUDE
The angle of the lateral axis relative to the horizon.

BANNER CLOUD
A cloud plume often observed to extend downwind from mountain peaks, even on otherwise cloud-free days.

BARO-AIDING
A method of augmenting the GPS integrity solution by using a nonsatellite input source. To ensure that baro-aiding is available, the current altimeter setting must be entered as described in the operating manual.

BAROGRAPH
Instrument for recording pressure as a function of time. Used by glider pilots to verify flight performance for badge or record flights.

BAROMETRIC SCALE
A scale on the dial of an altimeter to which the pilot sets the barometric pressure level from which the altitude shown by the pointers is measured.

BASE LEG
A flight path at right angles to the landing runway off its approach end. The base leg normally extends from the downwind leg to the intersection of the extended runway centerline.

BASIC EMPTY WEIGHT
The weight of the standard rotorcraft, operational equipment, unusable fuel,and full operating fluids, including full engine oil.

BASIC EMPTY WEIGHT (GAMA)
Basic empty weight includes the standard empty weight plus optional and special equipment that has been installed.

BASIC NEED
A perception factor that describes a person’s ability to maintain and enhance the organized self.

BASIC RADAR SERVICE
These services are provided for VFR aircraft by all commissioned terminal radar facilities. Basic radar service includes safety alerts, traffic advisories, limited radar vectoring when requested by the pilot, and sequencing at locations where procedures have been established for this purpose and/or when covered by a letter of agreement. The purpose of this service is to adjust the flow of arriving IFR and VFR aircraft into the traffic pattern in a safe and orderly manner and to provide traffic advisories to departing VFR aircraft. b.

BASKET
That portion of a hot air balloon that carries the pilot, passengers, cargo, fuel, and instruments.

BATTENS
The airfoil ribs of a WSC that are removed to foldup the wing.

BC
See back course.

BEACHING
Pulling a seaplane up onto a suitable shore so that its weight is supported by relatively dry ground rather than water.

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.)

BEAUFORT WIND SCALE
A standardized scale ranging from0-12 correlating the velocity ofthe wind with predictable surface features of the water.

BEHAVIORISM
Theory of learning that stresses the importance of having a particular form of behavior reinforced by someone other than the student to shape or control what is learned.

BELOW MINIMUMS
Weather conditions below the minimums prescribed by regulation for the particular action involved; e.g., landing minimums, takeoff minimums.

BERNOULLI’S PRINCIPLE
A principle that explains how the pressure of a moving fluid varies with its speed of motion. An increase in the speed of movement causes a decrease in the fluid’s pressure.

BEST GLIDE
The airspeed at which the aircraft glides the furthest for the least altitude lost when in non-powered flight.

BEST GLIDE SPEED (BEST L/D SPEED)
The airspeed that results in the least amount of altitude loss over a given distance. This speed is determined from the performance polar. The manufacturer publishes the best glide (L/D) airspeed for specified weights and the resulting glide ratio. For example, a glide ratio of 36:1 means that the glider will lose 1 foot of altitude for every 36 feet of forward movement in still air at this airspeed.

BEST-ANGLE-OF-CLIMB SPEED (VX)
The speed at which the aircraft produces the most gain in altitude in a given distance.

BEST-RATE-OF-CLIMB SPEED (VY)
The speed at which the aircraft produces the most gain in altitude in a given amount of time.

BILGE
The lowest point inside a float, hull, or water tight compartment.

BILGE PUMP
A pump used to extract water that has leaked into the bilge of a float or flying boat.

BIPLANES
Airplanes with two sets of wings.

BLADE CONING
An upward sweep of rotor blades as a result of liftand centrifugal force.

BLADE DAMPER
A device attached to the drag hinge to restrain the fore and aft movement of the rotorblade.

BLADE FEATHER OR FEATHERING
The rotation of the blade around the spanwise (pitch change)axis.

BLADE FLAP
The ability of the rotor blade to move in a vertical direction. Blades may flap independently or in unison.

BLADE GRIP
The part of the hub assembly to which the rotor blades are attached, sometimes referred to as blade forks.

BLADE LEAD OR LAG
The fore and aft movement of the blade in the plane of rotation. It is sometimes called hunting or dragging.

BLADE LOADING
The load imposed on rotor blades, determined by dividing the total weight of the helicopter by the combined area of all the rotor blades.

BLADE ROOT
The part of the blade that attaches to the blade grip.

BLADE SPAN
The length of a blade from its tip to its root.

BLADE STALL
The condition of the rotor blade when it is operating at an angle of attack greater than the maximum angle of lift.

BLADE TIP
The further most part of the blade from the hub of the rotor.

BLADE TRACK
The relationship of the blade tips in the plane of rotation. Blades that are in track will move through the same plane of rotation.

BLADE TRACKING
The mechanical procedure used to bring the blades of the rotor into a satisfactory relationship with each other under dynamic conditions so that all blades rotate on a common plane.

BLADE TWIST
The variation in the angle of incidence of a blade between the root and the tip.

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.

BLAST VALVE
The valve on a propane burner that controls the flow of propane burned to produce heat.

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.)

BLOCK ALTITUDE
A block of altitudes assigned by ATC to allow altitude deviations; for example, “Maintain block altitude 9 to 11 thousand.”

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.

BLOWBACK
The tendency of the rotor disc to tilt aft in forward flight as a result of flapping.


BOOKMARK
A means of saving addresses on the World Wide Web (WWW) for easy future access. Usually done by selecting a button on the web browser screen, it saves the current web address so it does not have to be input again in a lengthy series of characters.

BORA
A fall wind whose source is so cold that when the air reaches the lowlands or coast the dynamic warming is insufficient to raise the air temperature to the normal level for the region; hence, it appears as a cold wind.

BOUNDARY LIGHTS
Lights defining the perimeter of an airport or landing area. (Refer to AIM.)

BOWLINE KNOT
Pronounced boh' lin. A common knot that is easy to tie and untie and will not slip.

BPS
See ballistic parachute system.

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. (See RUNWAY CONDITION READING.)

BRAKING ACTION ADVISORIES
When tower controllers have received runway braking action reports which include the terms “fair,” “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” on the ATIS broadcast. 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.

BRANCHING
A programming technique which allows users of interactive video, multimedia courseware, or online training to choose from several courses of action in moving from one sequence to another.

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.

BRIEFING
An oral presentation where the speaker presents a concise array of facts without inclusion of extensive supporting material.

BROADCAST
Transmission of information for which an acknowledgement is not expected. (See ICAO term BROADCAST.)

BROADCAST [ICAO]
A transmission of information relating to air navigation that is not addressed to a specific station or stations.

BTU (BRITISH THERMAL UNIT)
A measurement of heat. The amount of heat required to raise 1 pound of water from 60 to 61 °F.

BUILDING BLOCK CONCEPT
Concept of learning that new knowledge and skills are best based on a solid foundation of previous experience and/or old learning. As knowledge and skills increase, the base expands, supporting further learning.

BULKHEAD
A structural partition that divides a float or a flyingboat hull into separate compartments and provides additional strength.

BUNTOVER
The tendency of a gyroplane to pitch forward when rotorforce is removed.

BUOYANCY
The tendency of a body to float or to rise when submerged in a fluid.

BUOYS
Floating objects moored to the bottom to mark a channel, waterway, or obstruction.

BURN
A common term meaning to activate the main blast valve and produce a full flame for the purpose of heating the air in the envelope.

BURNER
See Heater.

BYPASS RATIO
The ratio of the mass airflow in pounds per second through the fan section of a turbofan engine to the mass airflow that passes through the gas generator portion of the engine.