During power-off stalls with flaps full down, the stall occurs at a speed less than the minimum limit of the white arc on the indicator. This is most probably due to?

The correct answer reflects that the stall speed can be influenced by various factors, including how accurately the airspeed is being measured. The pitot-static system is responsible for providing accurate airspeed indications to the pilot. If there is an installation error within this system—such as a blockage or improper alignment—it can lead to incorrect readings on the airspeed indicator.

When performing power-off stalls, particularly with flaps fully deployed, a pilot should expect that stall speed would generally be within a certain range, typically indicated on the airspeed tape. If the stall occurs at a speed that is below what is normally expected (as indicated by the white arc for flaps extended operations), this discrepancy could suggest that the readings provided by the airspeed indicator are incorrect. An installation error in the pitot-static system could result in a false representation of airspeed, leading the pilot to misinterpret stall conditions.

In contrast, while airspeed indicator malfunctions can indeed cause discrepancies, true installation errors in the pitot-static system are more specifically tied to the condition described. High density altitude conditions would typically affect aircraft performance, but it would not directly cause an erroneous stall speed reading as indicated by the airspeed indicator.