- For a a pilot, a barometer is used as a part of their altimeter (the instrument that tells them the altitude at which they are flying). This instrument is calibrated to local altitude settings by setting a window (the Kollsman window) to the local altimeter setting. The local altimeter setting is the equivalent barometric pressure present.This guarantees the pilot will have accurate altimeter readings in relation to local terrain.
- During flight, pilots are regularly given local altimeter settings by air traffic controllers or by tuning into weather reporting stations. Maintaining correct local altimeter settings guarantees pilots of different aircraft are using the same settings to keep aircraft separated during flight by maintaining correct altitude calculations.
- Above 18,000 feet, all aircraft set their altimeter (barometric) settings in their instruments to a standard pressure of 29.92 inches mercury. This guarantees all pilots are on the same instrument settings.
- Aircraft performance is affected by air density and pressure. Barometric pressure also can be used in calculation charts for aircraft when determining air density and pressure altitude in relation to actual ground elevation. As air density decreases and pressure or density altitude increases, aircraft require additional distance for takeoff performance. Current local barometric pressure is used by a pilot in takeoff performance calculations.
- While slightly simplified, barometric pressure changes are also monitored by pilots to indicate general weather trends. Rising barometric pressures indicated improving weather (generally associated with high-pressure weather systems) while decreasing pressure generally indicates stormy weather (low-pressure weather systems). Lack of change in barometric pressure over time indicates stable weather conditions such as stalled or stationary weather fronts.
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