4/20/23 

Pilot/Controller Glossary 

MICROBURST

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 A small downburst with outbursts of damaging winds extending 2.5 miles or less. In spite of 

its small horizontal scale, an intense microburst could induce wind speeds as high as 150 knots 

(Refer to AIM.) 

MICRO-EN ROUTE AUTOMATED RADAR TRACKING SYSTEM (MEARTS)

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 An automated radar and 

radar beacon tracking system capable of employing both short-range (ASR) and long-range (ARSR) radars. This 

microcomputer driven system provides improved tracking, continuous data recording, and use of full digital 

radar displays. 
MID RVR

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(See VISIBILITY.) 

MIDDLE COMPASS LOCATOR

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(See COMPASS LOCATOR.) 

MIDDLE MARKER

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 A marker beacon that defines a point along the glideslope of an ILS normally located at 

or near the point of decision height (ILS Category I). It is keyed to transmit alternate dots and dashes, with the 

alternate dots and dashes keyed at the rate of 95 dot/dash combinations per minute on a 1300 Hz tone, which 

is received aurally and visually by compatible airborne equipment. 

(See INSTRUMENT LANDING SYSTEM.) 
(See MARKER BEACON.) 
(Refer to AIM.) 

MILES-IN-TRAIL

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A specified distance between aircraft, normally, in the same stratum associated with the 

same destination or route of flight. 
MILITARY AUTHORITY ASSUMES RESPONSIBILITY FOR SEPARATION OF AIRCRAFT (MARSA)

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A condition whereby the military services involved assume responsibility for separation between participating 

military aircraft in the ATC system. It is used only for required IFR operations which are specified in letters of 

agreement or other appropriate FAA or military documents. 
MILITARY LANDING ZONE

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 A landing strip used exclusively by the military for training. A military landing 

zone does not carry a runway designation. 
MILITARY OPERATIONS AREA

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(See SPECIAL USE AIRSPACE.) 

MILITARY TRAINING ROUTES

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 Airspace of defined vertical and lateral dimensions established for the 

conduct of military flight training at airspeeds in excess of 250 knots IAS. 

(See IFR MILITARY TRAINING ROUTES.) 
(See VFR MILITARY TRAINING ROUTES.) 

MINIMA

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(See MINIMUMS.) 

MINIMUM CROSSING ALTITUDE (MCA)

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 The lowest altitude at certain fixes at which an aircraft must cross 

when proceeding in the direction of a higher minimum en route IFR altitude (MEA). 

(See MINIMUM EN ROUTE IFR ALTITUDE.) 

MINIMUM DESCENT ALTITUDE (MDA)

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 The lowest altitude, expressed in feet above mean sea level, to 

which descent is authorized on final approach or during circle-to-land maneuvering in execution of a standard 

instrument approach procedure where no electronic glideslope is provided. 

(See NONPRECISION APPROACH PROCEDURE.) 

MINIMUM EN ROUTE IFR ALTITUDE (MEA)

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 The lowest published altitude between radio fixes which 

assures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes. 

The MEA prescribed for a Federal airway or segment thereof, area navigation low or high route, or other direct 

PCG M

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