Which mounting location helps sample undisturbed air for pitot-static measurements?

• A. The engine intake
• B. The wingtip
• C. Undisturbed air away from boundary layer
• D. The tailcone

Answer: (C)

Accurate pitot-static readings come from sampling air that is not disturbed by the aircraft’s surfaces. The pitot tube measures stagnation pressure and the static ports measure ambient pressure, so both need to see true free-stream air. The boundary layer—the thin layer of air hugging the fuselage and wings—moves slower and has pressure variations that differ from the outside air. If you place sensing for these pressures inside or near that boundary layer, the readings will be biased and unreliable, leading to incorrect airspeed and altitude indicators. Locations like the engine intake or tailcone are affected by engine flow and wake, and the wingtip encounters vortices and other disturbances. Mounting the probes in undisturbed air away from the boundary layer—such as on a forward mast or nose area—ensures the flow is clean and representative of the true air conditions, giving accurate pitot-static measurements.