Question

In which conditions would you expect the aircraft to be flying lower than their true altitude?

a) High pressure then set
b) Warm temperature
c) Low pressure then set
d) Dry weather

Answer 1

Aircraft may fly lower than their true altitude in conditions of low pressure. This difference occurs because altimeters are calibrated based on standard pressure conditions, and variations from these conditions without readjustment can lead to incorrect altitude readings.

Step-by-step explanation:

You would expect an aircraft to be flying lower than their true altitude in a low-pressure system. This is because, under a low-pressure condition, the density of the air is less, and altimeters, which measure altitude, are calibrated for standard pressure conditions at sea level. When an aircraft flies into an area of lower pressure without adjusting the altimeter setting, the instrument will indicate a higher altitude than the aircraft is actually flying at. Therefore, the pilot may be flying at an altitude lower than what the altimeter reads.

Essentially, if an altimeter is set at a higher pressure than the current atmospheric pressure, the actual flying altitude will be lower than what the altimeter shows. The opposite occurs with high pressure; if the altimeter is set based on a higher pressure, the pilot will be flying higher than the indicated altitude. It's the change in pressure that causes these discrepancies, not temperature, humidity, or weather conditions such as rain or dry weather.