M
m Meter m/s Meter per Second MAC Medium Access Controller Mach Number Mach number is the ratio of the true airspeed to the
speed of sound at a particular flight condition. It is the chief criterion of airflow pattern and is usually represented by the free-stream steady-state value.
Mag Magnetic
Magnetic  The bearing with respect to magnetic north. 
Bearing 
Magnetic  The direction north as determined by the earth’s mag 
North  netic field. The reference direction for measurement 
of magnetic directions. 
MAMS  Military Airspace Management System 
MAR  Managed Arrival Reservoir 
Marker  A transmitter operating at 75 MHz that provides iden 
Beacon  tification of a particular position along an airway or 
on the approach to an instrument runway. The mark 
er beacon is continuously tone-modulated by a 400-
Hz,a 1300-Hz or a 3000-Hz tone. Marker beacons 
along an instrument runway provide along-course 
(range) guidance and designate when an aircraft 
should be at a certain altitude if the aircraft is follow 
ing the glidepath. 
MASPS  Minimum Aviation System Performance Standards 
MAT  Maintenance Access Terminal 
MAWP  Missed Approached Waypoint 
MB  Marker Beacon 
MBE  Multiple Bit Error 
MC  Master Change 
MCB  Microwave Circuit Board 
MCC  Maintenance Control Computer 
MCDP  Maintenance Control Display Panel 
MCDU  Multifunctional Control Display Unit 
MCN  Manufacturing Control Number 
MCP  (1) Maintenance Control Panel 
(2) Mode Control Panel 
MCT  Max Continuous Thrust 
MCU  (1) Modular Concept Unit (approximately 1/8-ATR, 
Airline Transport Rack) 
(2) Multifunction Concept Unit 

MD11  Boeing Model 11 Aircraft (formerly McDonnell 
Douglas) 
MD90  Boeing Model 90 Aircraft (formerly McDonnell