Density error is caused by

• A. Nonstandard pressure and humidity
• B. Humidity changes
• C. Altitude changes
• D. Wind shear

Answer: (A)

Density error happens when the air density the Pitot-static system assumes doesn’t match the actual air density outside. The indicator is calibrated for standard atmosphere density, so any departure from that—especially changes in ambient pressure and humidity—throws off the relationship between dynamic pressure and actual speed. Pressure deviations change density directly, and humidity also alters density because moist air is lighter than dry air at the same pressure and temperature. So, nonstandard pressure and humidity cause the density the system uses to differ from reality, leading to density error. Humidity changes alone affect density, but the combination of pressure and humidity deviations best explains why the reading becomes inaccurate. Wind shear and altitude changes influence readings indirectly, but the root cause described here is the nonstandard pressure and humidity.