Transition altitude

From Wikipedia, the free encyclopedia

Transition altitude is the maximum altitude at which an aircraft should use an altimeter pressure setting indicating height above mean sea level (QNH)^[1]. Above the transition altitude (TA) the aircraft altimeter pressure setting should be adjusted to the standard pressure setting of 1013.25 hectopascals (millibars) or 29.92 inches of mercury and aircraft altitude will be specified as a flight level.

In the USA and Canada, the transition altitude is 18,000ft. In Europe, the transition altitude varies and can be as low as 3,000ft. There are discussions to standardise the transition altitude within the Eurocontrol area^[2].

Table for determining transition level

QNH (in millibars)	Transition altitude (in feet)
	3,000	4,000	5,000	6,000	18,000
1032-1050	FL25	FL35	FL45	FL55	FL175
1014-1032	FL30	FL40	FL50	FL60	FL180
996-1013	FL35	FL45	FL55	FL65	FL185
978-995	FL40	FL50	FL60	FL70	FL190
960-977	FL45	FL55	FL65	FL75	FL195
943-959	FL50	FL60	FL70	FL80	FL200

Transition level is the lowest flight level above the transition altitude. The table on the right shows the transition level according to transition altitude and QNH. When descending below the transition level, the pilot starts to refer to altitude of the aircraft by setting the altimeter to the QNH for the region or airfield. Note that the transition level is, by definition, less than 500ft above the transition altitude. Aircraft are not normally assigned to fly at the transition level as this does not guarantee separation from other traffic flying (on QNH) at the transition altitude; the lowest usable flight level is the transition level plus 500 feet.

Transition layer is the airspace between the transition altitude and the transition level.

[edit] References

1. ^ CAP 410 Manual of Flight Information Services. UK Civil Aviation Authority. Retrieved on 27 February, 2008.
2. ^ A Common European Transition Altitude; An ATC perspective. Eurocontrol. Retrieved on 27 February, 2008.