FAA Ground School Practice Test

Under what condition is indicated altitude the same as true altitude?

1. When flying above 10,000 feet

2. When at sea level under standard conditions

3. When in warmer than standard temperatures

4. When the altimeter is not calibrated

The correct answer is: When at sea level under standard conditions

Indicated altitude is the same as true altitude when at sea level under standard atmospheric conditions. At sea level, the standard atmospheric pressure is set at 29.92 inches of mercury, and the temperature is considered to be 15 degrees Celsius. Under these conditions, the altimeter, which measures the atmospheric pressure to determine altitude, will accurately reflect the true altitude because there are no variations in temperature or pressure that would otherwise cause deviations between indicated and true altitudes. In contrast, at altitudes above sea level or in uncommon atmospheric conditions, the relationship between indicated altitude and true altitude can vary due to factors such as pressure changes or temperature gradients. For example, when flying above 10,000 feet, variations in atmospheric pressure and temperature are more prevalent, leading to discrepancies between indicated and true altitudes. Additionally, warmer than standard temperatures will typically result in indicated altitudes being lower than true altitude, while a miscalibrated altimeter (not calibrated) can further distort the accurate altitude readings. Thus, the specific condition that aligns indicated and true altitude is indeed being at sea level under standard conditions.