Sea Level - Aviation


Using pressure to measure altitude results in two other types of altitude. Distance above true or MSL (mean sea level) is the next best measurement to absolute. MSL altitude is the distance above where sea level would be if there were no land. If one knows the elevation of terrain, the distance above the ground is calculated by a simple subtraction.

An MSL altitude—called pressure altitude by pilots—is useful for predicting physiological responses in unpressurized aircraft (see hypoxia). It also correlates with engine, propeller, and wing performance, which all decrease in thinner air.

Pilots can estimate height above terrain with an altimeter set to a defined barometric pressure. Generally, the pressure used to set the altimeter is the barometric pressure that would exist at MSL in the region being flown over. This pressure is referred to as either QNH or "altimeter" and is transmitted to the pilot by radio from air traffic control (ATC) or an Automatic Terminal Information Service (ATIS). Since the terrain elevation is also referenced to MSL, the pilot can estimate height above ground by subtracting the terrain altitude from the altimeter reading. Aviation charts are divided into boxes and the maximum terrain altitude from MSL in each box is clearly indicated. Once above the transition altitude (see below), the altimeter is set to the international standard atmosphere (ISA) pressure at MSL which is 1013.2 HPa or 29.92 inHg.

Read more about this topic:  Sea Level

Other articles related to "aviation":

Edwin Albert Link - Aviation
... Link, whom he had married in 1931, Edwin Link managed the very successful Link Aviation, Inc ... In 1976, he was inducted into the National Aviation Hall of Fame ...
Aviation - Environmental Impact
... In addition, there are environmental impacts specific to aviation Aircraft operating at high altitudes near the tropopause (mainly large jet airliners) emit aerosols and leave contrails ...
Naval Aviation
... Naval aviation is the application of manned military air power by navies, including ships that embark fixed-wing aircraft or helicopters ... In contrast, maritime aviation is the operation of aircraft in a maritime role under the command of non-naval forces such as the former RAF Coastal Command or a nation's coast guard ... naval aviation ...
Naval Aviation - History
... naval aviation began with pioneer aviator Glenn Curtiss who contracted with the Navy to demonstrate that airplanes could take off from and land aboard ships at sea ... Hibernia then transferred her aviation equipment to battleship London ... However, shipboard naval aviation had begun in the Royal Navy, and would become a major part of fleet operations by 1917 ...
Swissair - History - Founding Years
... The founding fathers were Balz Zimmermann and the Swiss aviation pioneer Walter Mittelholzer ... Two days later, Swissair's aviation was closed completely ... On July 30, 1945 Swissair was able to resume commercial aviation ...