EASA learning objective 022.02.01.02.02 states the follow with regards to pitot/static pressure sources: ' For each of these indicate the various locations and describe the following associated errors and how to correct, minimise the effect of or compensate for them: position errors; instrument errors; errors due to a non-longitudinal axial flow (including manoeuvre-induced errors).'

Position (pressure) error only applies when an aircraft is in motion and is caused by the true external static pressure not being sensed correctly. A false static pressure can be caused by the effect of distubed airflow passing over the static ports. The error is generally negligible at low speeds but can become significant at high speeds, during manoeuvres or when the angle of attack changes during gear and flap extension.

The size of the error can be mitigated by the design and location of the static port but it can never be completely eliminated. Correctly aligned pitot tubes, which are positioned outside the boundary layer suffer from negligible position error but because the instruments that they feed (ASI/Machmeter) are also fed static pressure then position error still needs to be accounted for in their indications..

Modern aircraft with air data computers can correct this predictable position error, correction tables are published for all other scenarios.

Note: Altimeter setting has no influence on position error