During flight, if the altimeter setting changes from 29.90 inches to 30.30 inches, how will the altimeter read?

When the altimeter setting changes from 29.90 inches to 30.30 inches, the altimeter will indicate a lower altitude than the actual altitude being flown. This is because a higher altimeter setting indicates that the atmospheric pressure is greater, which corresponds to a lower density altitude.

When the altimeter is set to a lower pressure like 29.90, the altimeter reads a higher altitude based on the lesser pressure. Elevating the pressure setting to 30.30 inches means that the altimeter must adjust downward to reflect this change in atmospheric pressure. Therefore, in this case, the altimeter would read approximately 400 feet lower than the actual altitude, leading to the conclusion that the reading is 400 feet too low.

It is essential to regularly update the altimeter setting to ensure accurate altitude readings, especially during changes in weather patterns or when crossing various airspace boundaries.