How many instruments use static pressure?

• A. Two
• B. One
• C. All three
• D. Three

Answer: (D)

Static pressure is the ambient air pressure that the system uses as a reference. The instruments that rely on this ambient pressure are three: the airspeed indicator, which measures dynamic pressure from the pitot tube relative to static pressure to show airspeed; the altimeter, which uses static pressure acting on sealed diaphragms to indicate altitude; and the vertical speed indicator, which tracks the rate of change in static pressure to display climb or descent rate. Because each of these three uses static pressure in its operation, three instruments use static pressure. Other instruments, like the attitude indicator, are powered independently (vacuum or electric) and don’t rely on static pressure for their primary indication.