Illustrations from the presentation at the ACM meeting help clarify the proposed change. This new definition would also align with that used by ICAO. The FAA project seeks to redefine mountainous areas more specifically as:ĭesignated mountainous areas include those areas having a terrain elevation differential exceeding 3,000 feet within 10 nautical miles within those one arc-second quadrangles overlying terrain or U.S.
This issue has become more important as we evolve to GPS navigation that supports direct RNAV routes and as ATC applies ADSB to its surveillance capabilities. Because the current DMA, especially in the West, covers such a large area, the MEAs for airways and minimum IFR altitudes that ATC must use can be unnecessarily high in regions such as central Washington and Oregon and similar wide valleys and basins in other states. In a DMA, the minimum altitudes for IFR flight (explicitly defined in 14 CFR §91.177) must be 2,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown. Another swath covers the high terrain from Alabama to New England, with exceptions in New York and Maine. In general, the western third of the U.S., with a couple of exceptions in the Central Valley of California and part of the Puget Sound region near Seattle, is designated as a mountainous area.
The project was a topic at the October 2020 session of the Aeronautical Charting Meeting the images below come from an FAA presentation at that meeting.įirst, some background. and in sections of higher terrain in the East. FAA is working on a long-term project to redefine Designated Mountainous Areas, a change that could allow lower IFR altitudes in many parts of the western U.S.
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