Definition
An error in airspeed and altitude indications caused by the static port sensing a pressure that differs slightly from true outside (ambient) static pressure. The disturbance comes from the aircraft's own shape and the airflow around it, and the error changes with airspeed, angle of attack, and aircraft configuration (flaps, gear, sideslip).
Plain English
The static port can never sit in perfectly undisturbed air, so the pressure it senses is slightly off. That small pressure offset shows up as a small error in the airspeed indicator and altimeter. The size of the error changes depending on how the aircraft is flying.
Context Anchor
Seen in pitot-static instrument discussions, aircraft flight manual correction tables, and airspeed or altitude accuracy checks.
Derivation
Called 'position error' because it comes from the position of the static port on the airframe — no location on the aircraft is in perfectly undisturbed air, so wherever the port is placed, some error results.
Why Pilots Care
Uncorrected position error leads to inaccurate airspeed and altitude indications that affect performance calculations, stall warning margins, and instrument flight safety.
Grounding Statement
If the airplane’s body disturbs the airflow near a pressure-sensing opening, the instrument may sense pressure that is not quite the same as the free air outside that disturbed area.
Intuition Check
Position error does not mean your navigation position is wrong. Here, “position” means the placement of the pressure-sensing openings on the aircraft.
Example Sentence 1
At low airspeeds with full flaps, position error can cause the indicated airspeed to read several knots off from the calibrated value.
Example Sentence 2
The mechanic adjusted the static port location to reduce position error before the next certification flight.