Which configuration is likely to give slightly erroneous readings to the static instruments?

• A. High AOA with flaps
• B. Level cruise with zero AoA
• C. Full power with retracts
• D. Clean wing at high speed

Answer: (A)

Static pressure readings are most reliable when the airflow around the aircraft and the static ports is undisturbed. In a configuration with a high angle of attack and flaps extended, the airflow becomes turbulent and the pressure field around the fuselage is distorted. This local distortion means the static ports sense a pressure that is not the true ambient static pressure, causing slight errors in the readings of the altimeter and vertical speed indicator (and, by extension, any indication that relies on static pressure).

In contrast, level flight with zero angle of attack generally provides smooth, undisturbed flow over the fuselage, so the static ports read near ambient pressure and the instruments stay accurate. A clean wing at high speed also tends to maintain stable, uniform flow, minimizing static-pressure biases. Full power with retracts can introduce some flow disturbances, but the most consistent source of static error among the options is the high angle of attack with flaps, which is known to disturb the static pressure field more noticeably.