8/15/19  Pilot/Controller Glossary  imminent and grave danger and that immediate  assistance is requested.  (See PAN-PAN.)  (Refer to AIM.)  MCA- MDA- MEA- MEARTS- (See MINIMUM CROSSING ALTITUDE.)  (See MINIMUM DESCENT ALTITUDE.)  (See MINIMUM EN ROUTE IFR ALTITUDE.)  (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.  (See METER FIX TIME/SLOT TIME.)  (See MINIMUM HOLDING ALTITUDE.)  (See MINIMUM IFR ALTITUDES.)  MFT- MHA- MIA- 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.  (See VISIBILITY.)  (See COMPASS LOCATOR.)  MID RVR- MIDDLE 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  PCG M-2 