imminent and grave danger and that immediate assistance is requested. 

 (See PAN-PAN.) 

 (Refer to AIM.) 

## MCA- 

(See MINIMUM CROSSING ALTITUDE.) 

## MDA- 

(See MINIMUM DESCENT ALTITUDE.) 

## MEA- 

(See MINIMUM EN ROUTE IFR ALTITUDE.) 

## MEARTS- 

(See MICRO-EN ROUTE AUTOMATED RADAR TRACKING SYSTEM.) 

METEOROLOGICAL IMPACT STATEMENT- 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 CTAS/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 FIX TIME/SLOT TIME (MFT)- A calculated time to depart the meter fix in order to cross the vertex at the ACLT. This time reflects descent speed adjustment and any applicable time that must be absorbed prior to crossing the meter fix. 

## METER LIST- 

(See ARRIVAL SECTOR ADVISORY LIST.) 

METER LIST DISPLAY INTERVAL- A dynamic parameter which controls the number of minutes prior to the flight plan calculated time of arrival at the meter fix for each aircraft, at which time the TCLT is frozen and becomes an ACLT; i.e., the VTA is updated and consequently the TCLT modified as appropriate until frozen at which time updating is suspended and an ACLT is assigned. When frozen, the flight entry is inserted into the arrival sector's meter list for display on the sector PVD/MDM. MLDI is used if filed true airspeed is less than or equal to freeze speed parameters (FSPD). 

METERING- A method of time-regulating arrival traffic flow into a terminal area so as not to exceed a predetermined terminal acceptance rate. 

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

METERING FIX- 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. 

METERING POSITION(S)- Adapted PVDs/ MDMs and associated “D” positions eligible for display of a metering position list. A maximum of four PVDs/MDMs may be adapted. 

METERING POSITION LIST- An ordered list of data on arrivals for a selected metering airport displayed on a metering position PVD/MDM. 

## MFT- 

(See METER FIX TIME/SLOT TIME.) 

## MHA- 

(See MINIMUM HOLDING ALTITUDE.) 

## MIA- 

(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.) 

MICRO-EN ROUTE AUTOMATED RADAR TRACKING SYSTEM (MEARTS)- 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 record- ing, and use of full digital radar displays. 

## MID RVR- 

(See VISIBILITY.) 

## MIDDLE COMPASS LOCATOR- 

(See COMPASS LOCATOR.) 

MIDDLE MARKER- 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 

