. Altitude

ltitude means the height above a certain surface or level. Air temperature and air pressure fall with increasing altitude. In aviation especially, altitude is measured from the ground at sea level.

Why Altitude Is Important

Altitude is important in aviation for sev­eral reasons. Aircraft need to fly at a minimum altitude that enables them to safely clear obstacles on the ground. Every aircraft also has a “flight ceiling,” or maximum altitude at which it may fly. This ceiling is determined by the
aircraft’s capabilities and by whether or not it has a pressurized cabin.

Large airliners, such as the Boeing 747 jumbo jet, cruise at altitudes from about 28,000 feet (8,530 meters) to

41,0 feet (12,500 meters). The big jets fly at standard altitudes called flight levels. The last two zeroes of a flight level are usually left out, so an altitude of 37,000 feet (11,280 meters) is known as Flight Level 370 to a pilot.

An important reason to measure alti­tude is to avoid collision with another aircraft. Aircraft must maintain vertical distance from each other to prevent accidents when they are flying in the same area. For airplanes traveling below

29.0 feet (8,840 meters), the standard vertical separation is 1,000 feet (305 meters). Aircraft above 29,000 feet (8,840 meters) maintain a vertical dis­tance of either 1,000 feet (305 meters) or

2.0 feet (610 meters).

To stay safe from collision, it is essential that all pilots are measuring altitude compared to the same level. Otherwise, two planes flying at the same altitude-but one flying over a hill while the other is over lower ground-would register different altitudes but, in reality, be in danger of colliding. To avoid this, aircraft in flight measure their altitude compared to a reference point called mean sea level (MSL). Charts and maps used by pilots show the heights of mountains and high ground as heights above mean sea level.