What causes density error?

• A. Altitude change
• B. Nonstandard pressure and temperature
• C. Humidity only
• D. Wind direction

Answer: (B)

Density error happens because the airspeed system assumes standard air density when converting pitot pressure to speed. The actual density of the air depends on pressure and temperature. When those values are not what the standard ISA assumes, the relationship between dynamic pressure and velocity changes, so the indicated airspeed differs from the true airspeed. Humidity can slightly affect density, but the primary cause is nonstandard pressure and temperature. Wind direction doesn’t affect the pitot-static readings, and altitude changes are what drive density changes overall, but the direct cause of density error is the nonstandard pressure and temperature.