minimum IFR altitude

Also found in: Acronyms.

minimum IFR altitude (MIA)

The lowest IFR (instrument flight rules) altitude established for use in a specific airspace. Depending on the airspace concerned, the minimum IFR altitude may be a minimum obstacle clearance altitude (MOCA), a minimum en route altitude (MEA), a minimum sector altitude (MSA), a minimum vectoring altitude (MVA), a geographic area safe altitude (GASA), a safe altitude 100 NM, a transition altitude, or a missed approach altitude. The minimum IFR altitude provides obstacle clearance but may or may not be within controlled airspace. Minimum altitudes are published on aeronautical charts. When minimum altitudes are not specified, the following rules apply:
i. In a designated mountainous area, 2000 ft above the highest obstacle within a horizontal distance of 5 statute miles from the course to be flown.
ii. In other than mountainous areas, 1000 ft above the highest obstacle within 5 statute miles from the course to be flown.
iii. In other cases, as authorized by ATC (air traffic control) or by the operator.
References in periodicals archive ?
At our home airport, unless the bases of the clouds were higher than the local minimum IFR altitudes (which is about 2800 feet), there would be no way to legally depart under the IFR umbrella (or get a "present position direct" clearance to any navaid or initial approach fix for an approach, either).
AIM, however, states you must comply with certain IFR criteria, including "minimum IFR altitudes."
This altitude clearance requires the pilot on an IFR flight to maintain VFR visibility and cloud clearances, follow the cleared routing, and authorizes the pilot to fly on his IFR flight plan at any valid VFR altitude (hemispheric rule) at or above the minimum IFR altitude. ATC may apply other restrictions, such as minimum or maximum altitudes.
You do, however, get to establish yourself on any published approach or descend to the minimum IFR altitude in order to reach VFR conditions for a visual landing.
Such a clearance is NOT AUTHORIZATION for the pilot to descend under IFR conditions below the minimum IFR altitude nor does it imply that ATC is exercising control over aircraft in Class G airspace; however, it provides a means for the aircraft to proceed to destination airport, descend, and land in accordance with applicable CFRs governing VFR flight operations.
Under these conditions, a cruise clearance without a crossing restriction authorizes a pilot to determine the minimum IFR altitude as prescribed in 14 CFR Section 91.177 and descend to it at pilot discretion if it is lower than the altitude specified in the cruise clearance.
* You must remain at or above minimum IFR altitudes (MEA, MOCA, MORA, etc.)
The flip side is the necessity to also operate under IFR regulations like minimum IFR altitudes, following your assigned route, required position reporting, adherence to all clearances, etc.
This translates to the availability of appreciably lower minimum IFR altitudes. Unfortunately, MVAs are not made public, so some help from local pilots and/or personal experience is necessary for relying on this method.
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