Final answer:
The rule for lowest usable flight levels and altimeter settings ensures safe separation between aircraft in the airspace. The International Civil Aviation Organization (ICAO) establishes a standard for vertical separation between aircraft, and pilots set their altimeters based on the local atmospheric pressure to obtain accurate altitude readings.
Step-by-step explanation:
The rule for lowest usable flight levels and altimeter settings helps ensure safe separation between aircraft in the airspace.
The International Civil Aviation Organization (ICAO) has established a standard for vertical separation between aircraft, known as the Vertical Separation Minimum (VSM). According to this standard, aircraft flying at or above 29,000 feet (FL290) use flight levels, with each flight level representing a difference of 100 feet in altitude. Below FL290, aircraft use altitudes, with each altitude representing a difference of 10 feet in altitude. This ensures that there is no confusion between aircraft operating at different altitudes.
Additionally, pilots need to set their altimeters correctly to ensure accurate altitude readings. They set their altimeters based on the local atmospheric pressure reported at the airport before departure or obtain the current altimeter setting while in flight from the air traffic control. This altimeter setting compensates for variations in atmospheric pressure and provides the pilot with an accurate indication of the aircraft's altitude above mean sea level.