Density error is caused by changes in what factors?

• A. Humidity changes
• B. Non-standard atmospheric condition
• C. Standard atmosphere
• D. No atmospheric change

Answer: (B)

Density error in the Pitot-static system happens because the airspeed indicator is calibrated for a specific air density, called ISA density. True airspeed depends on dynamic pressure, which is 0.5 times density times velocity squared. If the actual air density differs from what the instrument assumes, the same dynamic pressure points to a different true speed, so the reading is off. Non-standard atmospheric conditions change density by altering pressure, temperature, and humidity, and density can be expressed by rho = p / (R_specific * T), with humidity lowering density at a given temperature and pressure. Humidity changes are part of this overall effect, but the root cause is changes in non-standard atmospheric conditions, not a fixed standard atmosphere or no atmospheric change.