MAP-
(See MISSED APPROACH POINT.)
MARKER BEACON-An electronic navigation facility transmitting a 75 MHz vertical fan or boneshaped radiation pattern. Marker beacons are identified by their modulation frequency and keying code, and when received by compatible airborne equipment, indicate to the pilot, both aurally and visually, that he/she is passing over the facility.
(See INNER MARKER.)
(See MIDDLE MARKER.)
(See OUTER MARKER.)
(Refer to AIM.)
MARSA-
(See MILITARY AUTHORITY ASSUMES
RESPONSIBILITY FOR SEPARATION OF
AIRCRAFT.)

MAWP- Missed Approach Waypoint
MAXIMUM AUTHORIZED ALTITUDE- A pub-lished altitude representing the maximum usable altitude or flight level for an airspace structure or route segment. It is the highest altitude on a Federal airway, jet route, area navigation low or high route, or other direct route for which an MEA is designated in 14 CFR Part 95 at which adequate reception of navigation aid signals is assured.
MAYDAY- The international radiotelephony distress signal. When repeated three times, it indicates 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/HOST 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- 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.