Pitot-Static Instruments
Pitot-static usually include the altimeter, airspeed indicator, and vertical speed indicator. They operate using differences in the pressure of air coming from the static port and/or the pitot tube.
Alternate Static Source
Some airplanes are equipped with an alternate static source, which is often vented into the cockpit. This is used in case of an external static port blockage.
When an alternate static source is used:
- Airspeed Indicator: Will read greater actual airspeed
- Altimeter Higher than actual altitude
- Vertical Speed Indicator: Show a momentary climb, then stable