- ballistic parachute Emergency recovery parachute installed in (generally light) aircraft and capable of supporting both machine and occupants.
- band See radar frequency.
- bar Non-SI unit of pressure adopted by Jane's yearbook pending wider acceptance of Pa. 1 bar = 105 Pa. ISA pressure at S/L is 1013.2 mb or just over 1 bar. ICAO has standardised hectopascal for atmospheric pressure, in which ISA S/L pressure is 101.32 hPa.
- basic operating weight MTOW minus payload (thus, including crew, fuel and oil, bar stocks, cutlery and so on).
- bearingless rotor Rotor in which flapping, lead/lag and pitch change movements are provided by the flexibility of the structural material and not by bearings. No rotor is truly rigid.
- BITE Built-in test equipment.
- bladder tank Fuel (or other fluid) tank of flexible material.
- BLC Boundary-layer control.
- bleed air Hot high-pressure air extracted from gas turbine engine compressor or combustor and taken through valves and pipes to perform useful work such as pressurisation, driving machinery or anti-icing by heating surfaces.
- blown flap Flap across which bleed air is discharged at high (often supersonic) speed to prevent flow breakaway.
- BOW Basic operating weight (which see).
- BPR Bypass ratio.
- BTU Non-SI energy unit (British Thermal Unit) = 0.9478J.
- bulk cargo All cargo not packed in containers or on pallets.
- bus Busbar, main terminal in electronical system to which battery or generator power is supplied.
- BV Besloten Vennootschap (Netherlands company constitution).
- BVR Beyond visual range.
- BWB Blended wing/body.
- bypass ratio Air flow through fan duct (not passing through core) divided by airflow through core.
- byte Group of bits of information forming unit in computer processing.
