It seems that Asia are facing same issues as us:
International Civil Aviation Organization
The Seventh Meeting of the Regional Airspace Safety Monitoring Advisory Group (RASMAG/7)
Bangkok, Thailand, 4 – 8 June 2007
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Summary
This paper provides the definition of Large Height Deviation (LHD) and its causes for flight operations in the RVSM airspace.
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1. Introduction
1.1 For the past meetings of the RVSM implementation in the Asia Region, the issue of LHD has been discussed in great details due to the significant number of occurrences, especially in the RVSM airspace of Western Pacific/South China Sea (WPAC/SCS).
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2.2 The causes of LHD occurrence include:
• Operational errors (aircraft operating at a flight level other than the assigned flight level due to ATC/Pilot loop errors and incorrect clearance), which is categorized into three causes:
- Flight crew not following the correct ATC clearance
- ATC issuing an incorrect ATC clearance
- Receiving ATC unit unable to apply the separation standards during a transfer of control responsibility between two ATC units
• Aircraft contingency events occurring in situation where the pilot cannot initially follow normal contingency procedures and is forced to climb/descend through flight levels before diverting from track,
• Deviation due to the effect of high level meteorological condition, and
• Deviation due to Technical Collision Avoidance System (TCAS) advisories, which includes:
- Flight crew correctly following the TCAS Resolution Advisory (RA)*,
- Flight crew incorrectly following the TCAS RA, and
- Any vertical displacement not conforming to the resolution advisory.
2.3 It is important to note that the LHD resulting from actions complying with the TCAS RA would not reflect risk in the RVSM airspace since it is a proper remedial action of flight crew to prevent the possible mid-air collision between aircraft. Nonetheless, it is strongly recommended that all LHD occurrences related to TCAS advisory be reported to the responsible RMA for detailed airspace safety analyses.