How does altitude affect official altimeter readings during long flights?

• A. The altimeter readings are influenced by altimeter settings and ambient pressure; regular calibrations ensure accuracy.
• B. Altimeter readings are fixed and do not require adjustments.
• C. Altimeter automatically corrects for temperature without setting changes.
• D. Altimeter depends only on airspeed.

Answer: (A)

The key idea is that a barometric altimeter measures ambient pressure and converts it to an altitude reading using a reference pressure you dial in. The altitude shown depends on the current pressure setting you set (the local sea‑level pressure) and the actual ambient pressure in the air. To keep the reading accurate, pilots update the altimeter setting to the local pressure (and switch to the standard setting at higher flight levels when required) so the indicated altitude matches the aircraft’s true height above mean sea level. On long flights, pressure varies with weather systems and across regions, so without adjusting the setting, the indicated altitude would drift. The instrument doesn’t automatically correct for temperature, and it isn’t based on airspeed alone, so those factors don’t fix the reading. Regularly updating the altimeter setting and ensuring the instrument is properly calibrated keeps the readings accurate throughout the flight.