Private Pilot Private Exam

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

1. When at sea level under standard conditions

2. When in a controlled airspace

3. During a climb at standard temperature

4. When the altimeter setting is incorrect

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

Indicated altitude represents the altitude read directly from the altimeter, while true altitude is the actual height above mean sea level. These two values are the same under specific atmospheric conditions. Indicated altitude equals true altitude when flying at sea level under standard conditions, meaning the atmospheric pressure is at 29.92 inches of mercury (inHg) and the temperature is at 15 degrees Celsius (59 degrees Fahrenheit). Under these standard atmospheric conditions, the altimeter is properly calibrated to accurately reflect the actual altitude relative to mean sea level. At sea level, both indicated and true altitudes are zero, making them equal. In controlled airspace, while your altitude may be regulated, it doesn't inherently ensure that indicated and true altitude are the same. During a climb at standard temperature, the indicated altitude may change due to vertical movement, so it doesn’t remain equal to true altitude. If the altimeter setting is incorrect, indicated altitude will diverge from true altitude, causing discrepancies in the readings. Therefore, only under standard conditions at sea level is indicated altitude equal to true altitude.