What is the effect of flying at altitude with improper altimeter settings?

Flying at altitude with improper altimeter settings can indeed lead to altitude discrepancies, which poses a significant risk to safety. The altimeter is a vital instrument that provides pilots with their altitude above sea level. If the altimeter setting is incorrect, it may result in the aircraft being higher or lower than the pilot believes. This discrepancy can lead to dangerous situations, especially in congested airspace or near terrain where altitude awareness is crucial.

Altitude discrepancies can affect air traffic control's ability to provide separation between aircraft, potentially leading to mid-air collisions. Additionally, altitude misjudgments can cause the aircraft to inadvertently enter potentially hazardous airspace or terrain, resulting in dangerous flight situations.

The other options do not correctly reflect the implications of incorrect altimeter settings. For example, while speed readings can be affected by altitude, the primary concern with an incorrect altimeter setting relates directly to altitude awareness and safety. Fuel efficiency and visibility are not directly influenced by altimeter settings. Therefore, understanding the correct usage of altimeter settings is vital for maintaining safety during flight.