The Pitot-Static System
Three instruments, two pressure sources, one common failure mode. How the airspeed indicator, altimeter, and VSI actually work — and how they lie.
Three of the six primary flight instruments in a conventional cockpit — the airspeed indicator, altimeter, and vertical speed indicator — derive their readings from air pressure. Together they form the pitot-static system.
How each instrument is fed
| Instrument | Uses pitot | Uses static |
|---|---|---|
| Airspeed Indicator (ASI) | Yes | Yes |
| Altimeter | No | Yes |
| Vertical Speed Indicator (VSI) | No | Yes (rate of change) |
Failure modes
Because two of three instruments depend on the static source, a blocked static port takes out both the altimeter and the VSI while leaving the ASI reading — but reading wrong. Diagnosing the failure in flight means recognizing the pattern, not memorizing arrows.
The atmospheric physics behind these instruments is developed in Reading a METAR. For more airplane systems, see the Mechanical Systems hub.
Educational content, not flight instruction. Consult a certificated flight instructor and current official publications.
Questions & answers
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