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Why 90m ? - 2
11.11.2009
Submission:
It is historical. In 1951 the MOC was set to 300ft for NDB and VOR final approaches. Then in PANS-HAL in 1954 the VOR criteria was amended to 90m when the facility is not more than 6NM from the aerodrome, 120m if 6 to 8.7NM from the aerodrome and 150m if 8.7 to 10.4NM from the aerodrome. Then in 1979 in the PANS-OPS second edition the 75m value for procedures with a FAF was introduced. The rationale was that the FAF allowed an accurate definition of the aircraft position relative to the altimeter setting source and therefore any barometric pressure difference is less of a factor.Beat Zimmermann -Air Navigation Institute - Switzerland
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