The pitot tube(s) and static port(s) may be mounted in a position on the aircraft where the flow is affected by the presence of the aircraft, changes in configuration (flaps and maybe gear) and proximity to the ground (ground effect).
The position of the pitot tube(s) and static vent(s), together with the aircraft’s configuration (flaps, landing gear etc.) and attitude to the airflow (angle of attack and sideslip) will affect the pressures sensed, particularly the pressures sensed at the static vent(s).
