Definition
Atmospheric pressures that are reduced compared to sea-level standard pressure, encountered as altitude increases. As a pilot climbs, the weight of the air column above decreases, and the surrounding air pressure drops accordingly. At high altitudes, these reduced pressures can allow dissolved nitrogen in body tissues to come out of solution and form bubbles, producing decompression sickness (DCS).
Plain English
The thinner, lower-pressure air found at higher altitudes. The higher you go, the less the air pushes on you and on everything dissolved in your body.
Context Anchor
Seen in aeromedical discussions of high-altitude flight, unpressurized aircraft, cabin pressure loss, and altitude-induced decompression sickness.
Derivation
Barometric comes from the Greek 'baros' meaning weight, plus 'metron' meaning measure — literally 'weight measurement.' Barometric pressure is the measured weight of the atmosphere pressing down. 'Low' here refers to that pressure being reduced relative to sea-level standard, not to a low reading on a chart.
Why Pilots Care
Pilots must recognize that low barometric pressures at altitude raise the risk of decompression sickness during ascent or prolonged flight above certain levels.
Grounding Statement
The higher you fly, the less the atmosphere is pressing on you, and that drop in pressure is what makes high altitude physiologically dangerous.
Intuition Check
Do not read this as only meaning “low pressure weather” or a storm system. In this context, low barometric pressures mean reduced air pressure around the body, usually because of altitude or loss of cabin pressure.
Example Sentence 1
The low barometric pressures encountered above 18,000 feet increase the risk of decompression sickness, particularly for pilots who recently went scuba diving.
Example Sentence 2
Pre-flight planning included oxygen use to reduce the effects of low barometric pressures during the high-altitude portion of the trip.