Pilot/Controller Glossary 

12/2/21 

imminent and grave danger and that immediate 
assistance is requested.

 (See PAN-PAN.)
 (Refer to AIM.) 

MCA

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(See MINIMUM CROSSING ALTITUDE.) 

MDA

−

 

(See MINIMUM DESCENT ALTITUDE.) 

MEA

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(See MINIMUM EN ROUTE IFR ALTITUDE.) 

MEARTS

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(See MICRO-EN ROUTE AUTOMATED RADAR 

TRACKING SYSTEM.) 

METEOROLOGICAL IMPACT STATEMENT

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An unscheduled planning forecast describing 
conditions expected to begin within 4 to 12 hours 
which may impact the flow of air traffic in a specific 
center’s (ARTCC) area. 

METER FIX ARC

−

 A semicircle, equidistant from 

a meter fix, usually in low altitude relatively close to 
the meter fix, used to help TBFM/ERAM calculate a 
meter time, and determine appropriate sector meter 
list assignments for aircraft not on an established 
arrival route or assigned a meter fix. 

METER REFERENCE ELEMENT (MRE)

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 A 

constraint point through which traffic flows are 
managed. An MRE can be the runway threshold, a 
meter fix, or a meter arc. 

METER REFERENCE POINT LIST (MRP)

−

 A list 

of TBFM delay information conveyed to the 
controller on the situation display via the Meter 
Reference Point View, commonly known as the 
“Meter List.” 

METERING

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A method of time

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regulating traffic 

flows in the en route and terminal environments. 

METERING AIRPORTS

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 Airports adapted for 

metering and for which optimum flight paths are 
defined. A maximum of 15 airports may be adapted. 

METERING FIX

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 A fix along an established route 

from over which aircraft will be metered prior to 
entering terminal airspace. Normally, this fix should 
be established at a distance from the airport which 
will facilitate a profile descent 10,000 feet above 
airport elevation (AAE) or above. 

MHA

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(See MINIMUM HOLDING ALTITUDE.) 

MIA

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(See MINIMUM IFR ALTITUDES.) 

MICROBURST

−

 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.) 

MICRO­EN ROUTE AUTOMATED RADAR 
TRACKING SYSTEM (MEARTS)

−

 An automated 

radar and radar beacon tracking system capable of 
employing both short­range (ASR) and long­range 
(ARSR) radars. This microcomputer driven system 
provides improved tracking, continuous data record­
ing, 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.) 

MILES­IN­TRAIL

−

 A specified distance between 

aircraft, normally, in the same stratum associated 
with the same destination or route of flight. 

MILITARY AUTHORITY ASSUMES RESPONSI­
BILITY FOR SEPARATION OF AIRCRAFT 
(MARSA)

−

 A condition whereby the military 

services involved assume responsibility for separa­
tion 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. 

PCG M

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