Definition
Inaccuracies in indicated airspeed caused by the location of the static port (or pitot-static system) on the aircraft, where local airflow around the fuselage does not perfectly match the true free-stream pressure. Position error varies with airspeed, angle of attack, and aircraft configuration (flaps, gear, sideslip).
Plain English
The airspeed indicator reads slightly off because of where the sensors are mounted on the airplane. Air flowing around the fuselage gets disturbed, so the static port doesn't always sense perfectly accurate pressure, and the indicated airspeed is a little high or low as a result.
Context Anchor
Seen in airspeed indicator discussions, especially when comparing indicated airspeed with calibrated airspeed.
Derivation
Position' here refers to the physical location of the static port on the aircraft. The error is caused by where the sensor sits, not by the instrument itself — hence 'position error.'
Why Pilots Care
Uncorrected position errors produce false airspeed and altitude data that can lead to incorrect flight decisions during instrument maneuvers and approaches.
Grounding Statement
If airflow is bent, slowed, or sped up around the aircraft before it reaches a pressure opening, the instrument may sense slightly wrong pressure.
Intuition Check
Do not read position errors as mistakes in the aircraft’s geographic position. Here, position means the placement of the pressure-sensing openings on the aircraft.
Example Sentence 1
At slow approach speeds with full flaps, position error is largest, so the pilot checked the airspeed calibration table to find the calibrated airspeed.
Example Sentence 2
The airspeed calibration chart includes corrections for position errors at various speeds and flap settings.