Level bust
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A level bust, also known as an altitude deviation, occurs when an aircraft fails to fly at the level for which it has been cleared. A level bust is defined by EUROCONTROL as: "Any unauthorised vertical deviation of more than 300 feet from an ATC flight clearance." This may take one of three different forms: #An aircraft in level flight climbs or descends without clearance #An aircraft climbing or descending fails to level off accurately at the correct level (either passing through and continuing the climb or descent, or passing through and then returning to the correct level) #An aircraft levelling off at the correct level or altitude, but with an incorrect altimeter setting
A level bust, also known as an altitude deviation, occurs when an aircraft fails to fly at the level for which it has been cleared. A level bust is defined by EUROCONTROL as: "Any unauthorised vertical deviation of more than 300 feet from an ATC flight clearance." This may take one of three different forms: An aircraft in level flight climbs or descends without clearance An aircraft climbing or descending fails to level off accurately at the correct level (either passing through and continuing the climb or descent, or passing through and then returning to the correct level) An aircraft levelling off at the correct level or altitude, but with an incorrect altimeter setting
Accidents and serious incidents involving level bust
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. Neither aircraft was fitted with ACAS. 21 February 2001 , a level bust 10 nm north of Oslo by a climbing PIA A310 led to loss of separation with an SAS B736 in which response to a TCAS RA by the A310 not being in accordance with its likely activation(descend). The B736 received and correctly actioned a Climb RA. 24 November 2006, an A310 descended significantly below cleared altitude during radar vectored approach positioning, as a result of the flight crew's failure to set the QNH, which was very low.
References
See also
Level bust awareness e-learning toolkit
Text derived from https://en.wikipedia.org/w/index.php?oldid=1332102446 under CC BY-SA 4.0; modifications have been made.