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In ISA temperature conditions the altimeter will read the height above the airfield/runway in the vicinity of the airfield. SPS/STD - 'Standard Pressure Setting' or just 'Standard' refers to the altimeter being set to the standard pressure of 1013.25 hPa. It is the setting that causes an altimeter to read the aircraft's flight level (FL).
12 November 1996, an Il-76 collided in mid air with a Saudi B747 near New Delhi India, following a level bust by the Il-76.; 12 November 1996, a B737 descended below its assigned holding level in the LHR stack, in IMC, to within 100 feet vertically and between 680 and 820 metres horizontally of an MD-81 at its correct level.
QFF is the location value plotted on surface synoptic chart and is closer to reality than QNH, though it is only indirectly used in aviation. [citation needed] Another method [which?]: The derivation assumes that an isothermal layer at the station temperature extends to the sea level.
The altimeter setting used is the ISA surface pressure of 1013 hPa or (29.92 inHg). The actual surface pressure may vary from this at different locations and times. Therefore, by using a standard pressure setting, every aircraft has the same altimeter setting, and vertical clearance can be maintained. [1] Scale comparison of some flight level ...
In aviation, atmospheric sciences and broadcasting, a height above ground level (AGL [1] or HAGL) is a height measured with respect to the underlying ground surface.This is as opposed to height above mean sea level (AMSL or HAMSL), height above ellipsoid (HAE, as reported by a GPS receiver), or height above average terrain (AAT or HAAT, in broadcast engineering).
It indicates altitude obtained when an altimeter is set to an agreed baseline pressure under certain circumstances in which the aircraft’s altimeter would be unable to give a useful altitude readout. Examples would be landing at a high altitude or near sea level under conditions of exceptionally high air pressure.
En-route charts are divided into high and low versions, with information on airways and navaids for high- and low-altitude flight, respectively. The division between low altitude and high altitude is usually defined as the altitude that marks transition to flight levels (in the United States , this is taken to be 18,000 feet MSL by convention).
The altimeter is adjustable for local barometric pressure which must be set correctly to obtain accurate altitude readings, usually in either feet or meters. As the aircraft ascends, the capsules expand and the static pressure drops, causing the altimeter to indicate a higher altitude. The opposite effect occurs when descending.