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M&R: Maintenance and Repair (MTMC1)

M1FC: Model 1 Full Capacity (FAA20)

M5: Manual Five Speed (DOE6)

M85: 85 Percent / 15 Percent Unleaded Gasoline (BTS8)

MA: Minor Arterial (FHWA19)

MAA: Maximum Authorized Altitude (FAA20)

MAB: Medical Advisory Board (NHTSA7)

MAC: Maintenance Action Code (FAA20)

MAC: Mean Aerodynamic Cord (FAA20)

MAC: Military Airlift Command (MTMC1)

Mach Number: The ratio of true airspeed to the speed of sound. (14CFR1) (FAA4)

Mach Technique: Describes a control technique used by air traffic control whereby turbojet aircraft operating successively along suitable routes are cleared to maintain appropriate MACH numbers for a relevant portion of the en route phase of flight. The principle objective is to achieve improved utilization of the airspace and to ensure that separation between successive aircraft does not decrease below the established minima. (FAA4)

Mackinaw Boat: A crudely built flatboat used on the Ohio and Upper Mississippi rivers during the 18th century. (TNDOT1)

MADD: Mothers Against Drunk Driving (FHWA18)

MADT: Monthly ADT (FHWA19)

MADW: Monthly Average Days of the Week (FHWA19)

Magazine Vessel: A vessel used for the receiving, storing, or dispensing of explosives. (49CFR171)

MAGLEV: Magnetic Levitation (FHWA18)

Magnetic Levitation: A rail transportation system with exclusive right-of-way which is propelled along a fixed guideway system by the attraction or repulsion of magnets on the rails and under the rail cars. (APTA1)

Mail Revenue: Revenues from the carriage of mail bearing postage for air transportation both U.S. and foreign mail that go by air on priority and nonpriority bases. (BTS4)

Main: A distribution line that serves as a common source of supply for more than one gas service line. (AGA1)

Main Deck: The lowest deck on a river steamboat. The main deck supports the vessel's engines and boilers and has space for fuel and cargo. (TNDOT1)

Main Heating Fuel: Fuel that powers the main heating equipment. (DOE5)

Main Rotor: The rotor that supplies the principal lift to a rotorcraft. (14CFR1)

Main Stem: The main portion of navigable channel of a river where more than one channel exists. (TNDOT1)

Main Track: A track, other than an auxiliary track, extending through yards or between stations, upon which trains are operated by timetable or train order or both, or the use of which is governed by a signal system. (49CFR218) (49CFR221) (49CFR236) (49CFR245) (FRA3)

Mains (Gas): A network of pipelines that serves as a common source of supply for more than one gas service line. (BTS11)

Maintain: 1) Concerning altitude flight level, the term means to remain at the altitude flight level specified. The phrase "climb and" or "descend and" normally precedes "maintain" and the altitude assignment; e.g., "descend and maintain 5,000". 2) Concerning other Air Traffic Control (ATC) instructions, the term is used in its literal sense; (e.g., maintain Visual Flight Rule (VFR)). (FAA4)

Maintenance: All expenses, both direct and indirect, specifically identifiable with the repair and upkeep of property and equipment. (BTS4)

Maintenance Area: Maintenance area is any geographic region of the United States previously designated nonattainment pursuant to the CAA Amendments of 1990 and subsequently redesignated to attainment subject to the requirement to develop a maintenance plan under section 175A of the CAA, as amended. (FHWA21)

Maintenance Control Center: Responsible for the oversight of authorization for vehicle repair and authorization and certification of maintenance and repair invoices for Interagency Fleet Management System (IFMS) vehicles within the specified region(s). The MCC also contacts vendors to schedule vehicle services. (GSA2)

Major Alteration: An alteration not listed in the aircraft, aircraft engine, or propeller specifications that 1) Might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or 2) Done according to accepted practices cannot be done by elementary operations. (14CFR1)

Major Arterial Highway: A major highway used primarily for through traffic. (BTS13)

Major Carrier Group: Air carrier groups with annual operating revenues exceeding $1,000,000,000. (BTS4) (BTS5) (BTS6) (FAA11)

Major Collector: Collector roads that tend to serve higher traffic volumes than other collector roads. Major collector roads typically link arterials. Traffic volumes and speeds are typically lower than those of arterials. (BTS12)

Major Fuel: Fuels or energy sources such as electricity, fuel oil, liquefied petroleum gases, natural gas, district steam, district hot water, and district chilled water. (DOE5)

Major Interstate Pipeline Company: A company whose combined sales for resale, including gas transported interstate or stored for a fee, exceeded 50 million thousand cubic feet in the previous year. (DOE5)

Major Repair: A repair that, if improperly done, might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or that is not done according to accepted practices or cannot be done by elementary operations. (14CFR1)

Major River: A river that, because of its velocity and vessel traffic, would require a more rapid response in case of a worst case discharge. (49CFR194)

Majors (Air): Air carrier groups with annual operating revenues exceeding $1 billion. (BTS11)

Make Short Approach: Used by Air Traffic Control (ATC) to inform a pilot to alter his traffic pattern 80 degrees as to make a short final approach. (FAA4)

Make Up Tow: To assemble barges into a tow. (TNDOT1)

MALS: Medium Intensity Approach Lighting System (FAA20)

MALSF: Medium Intensity Approach Light System with Sequenced Flashers (FAA20)

MALSR: Medium-Intensity Approach Lighting System With Runway Alignment Indicator (FAA20)

MALSR: Medium Intensity Approach Light System With Rail (FAA4) (FAA17) (FAA19)

MAM: Maintenance Assumed Monitoring (FAA20)

MAMS: Military Airspace Management System (FAA7)

Man-Hour: An industrial unit of production reflecting paid labor hours. (FRA3)

Management Systems: (1) Systems to improve identification of problems and opportunities throughout the entire surface transportation network, and to evaluate and prioritize alternative strategies, actions and solutions. (2) A systematic process, designed to assist decision makers in selecting cost-effective strategies/actions to improve the efficiency and safety of, and protect the investment in, the nation's transportation infrastructure. (FHWA21)

Mandatory Altitude: An altitude depicted on an instrument approach procedure chart requiring the aircraft to maintain altitude at the depicted value. (FAA4)

Mandatory Use Seat Belt Law: A law requiring some adult occupants of some traffic vehicles to use available restraint systems. (NHTSA1)

Maneuver Boat: Boat used by the Corps of Engineers in raising and lowering movable wickets of dams on the Ohio River. (TNDOT1)

Maneuvering: Changing of course, speed, or similar boat handling action during which a high degree of alertness is required or the boat is imperiled because of the operation, i.e. docking, mooring, undocking, etc. (USCG2)

Maniac: Shop mechanic. (ATA1)

Manifold Pressure: Absolute pressure as measured at the appropriate point in the induction system and usually expressed in inches of mercury. (14CFR1)

Manner of Collision: A classification for crashes in which the first harmful event was a collision between two motor vehicles in transport. (NHTSA3)

Manual Interlocking: An arrangement of signals and signal appliances operated from an interlocking machine and so interconnected by means of mechanical and/or electric locking that their movements must succeed each other in proper sequence, train movements over all routes being governed by signal indication. (49CFR236)

Manual Restraint System: Occupant restraints that require some action, usually buckling, before they are effective. They include shoulder belt, lap belt, lap and shoulder belt, infant carrier, or child safety seat. (NHTSA1)

Manufacturer: 1) Any person engaged in the manufacture, construction, or assembly of boats or associated equipment 2) The manufacture or construction of components for boats and associated 3) Equipment to be sold for subsequent assembly or 4) The importation into the United States for sale of boats, associated equipment, or components thereof. (USCG1)

Manufacturer Identification Code: Three-character identifier assigned by Headquarters on request to those manufacturers and importers defined under 33 CFR 181.31. (USCG1)

MAP: Military Airport Plan (FAA17)

MAP: Maintenance Automation Program (FAA20)

MAP: Military Airport Program (FAA20)

MAP: Missed Approach Point (FAA20)

MAP: Missed Approach Procedure (FAA20)

MAP: Modified Access Pricing (FAA20)

MAP-21: Moving Ahead for Progress in the 21st Century (DOT2)

MAR: Minimally Attended Radar (FAA19)

MAR: Managed Arrival Reservoir (FAA7)

MARAD: Maritime Administration (BTS11)

MARDEZ: Maritime Defense Zones (MARAD4)

Marina: Establishments primarily engaged in operating marinas. These establishments rent boat slips and store boats, and generally perform a range of other services including cleaning and incidental boat repair. They frequently sell food, fuel, and fishing supplies, and may sell boats. (BOC1)

Marine Cargo Handling: Establishments primarily engaged in activities directly related to marine cargo handling from the time cargo, for or from a vessel, arrives at shipside, dock, pier, terminal, staging area, or in-transit area until cargo loading or unloading operations are completed. Included in this industry are establishments primarily engaged in the transfer of cargo between ship and barges, trucks, trains, pipelines, and wharfs. Cargo handling operations carried on by transportation companies and separately reported are classified here. This industry includes the operation and maintenance of piers, docks, and associated buildings and facilities. (BOC1)

Marine Pollutant: A hazardous material which is listed in Appendix B to CFR 172.101 of this subchapter and, when in a solution or mixture of one or more marine pollutants, is packaged in a concentration which equals or exceeds: 1) Ten percent by weight of the solution or mixture for materials listed in the appendix; or 2) One percent by weight of the solution or mixture for materials that are identified as severe marine pollutants in the appendix. (49CFR171)

Marine Sanitation Device: Any equipment for installation on board a vessel which is designed to receive, retrain, treat or discharge sewage and any process to treat such sewage. (USCG1)

Marine Terminal: A designated area of a port, which includes but not limited to wharves, warehouses, covered and/or open storage spaces, cold storage plants, grain elevators and/or bulk cargo loading and/or unloading structures, landings, and receiving stations, used for the transmission, care, and convenience of cargo and/or passengers in the interchange of same between land and water carriers or between two water carriers. (MARAD1)

Marine Terminal Operator: Person or entity that operates the various marine terminals at ports, usually under long-term lease agreements with local or state governments or port authorities. The marine terminal operator provides receiving and delivery, and other terminal services for the cargos moving through these facilities. (MARAD1)

Maritime: Business pertaining to commerce or navigation transacted upon the sea or in seaports in such matters as the court of admiralty has jurisdiction. (MARAD2)

Maritime Administration: The Maritime Administration was established by Reorganization Plan No. 21 of 1950 (5 U.S.C. app.) effective May 24, 1950. The Maritime Act of 1981 (46 U.S.C. 1601) transferred the Maritime Administration to the Department of Transportation, effective August 6, 1981. The Administration administers programs to aid in the development, promotion, and operation of the U.S. Merchant Marine. It is also charged with organizing and directing emergency merchant ship operations. It administers subsidy programs, provides financing guarantees for the construction, reconstruction, and reconditioning of ships; and enters into capital construction fund agreements that grant tax deferrals on moneys to be used for the acquisition, construction, or reconstruction of ships. The Administration constructs or supervises the construction of merchant type ships for the Federal Government, helps industry generate increased business for U.S. ships and conducts programs to develop ports, facilities, and intermodal transport, and to promote domestic shipping. The Administration conducts program and technical studies and administers a War Risk Insurance Program, and under emergency conditions the Maritime Administration charters Government-owned ships to U.S. operators, requisitions or procures ships owned by U.S. citizens, and allocates them to meet defense needs. It maintains a National Defense Reserve Fleet of Government-owned ships, regulates sales to aliens and transfers to foreign registry of ships that are fully or partially owned by U.S. citizens. It also operates the U.S. Merchant Marine Academy, Kings Point. (OFR1)

Maritime Carrier: Carriers which operate on the open sea, i.e., their operations must include a foreign or international component and may include a domestic component. (TNDOT1)

Maritime Revenue: Revenue received for operations in international or foreign shipping. (TNDOT1)

Mark Twain: Colloquial term for 12-foot depth or mark 2 on the lead line. (TNDOT1)

Marked Channel: Channel marked by buoys. (TNDOT1)

Marker Beacon: An electronic navigation facility transmitting a 76 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 is passing over the facility. (FAA4)

Marketed Production: Gross withdrawals less gas used for repressuring, quantities vented and flared, and nonhydrocarbon gases removed in treating or processing operations. Includes all quantities of gas used in field and processing operations. (DOE3)

Marking: A descriptive name, identification number, instructions, cautions, weight, specification, or combinations thereof, required by this subchapter on outer packagings of hazardous materials. (49CFR171)

MARSA: Military Assumes Responsibility for Separation (FAA20)

MARTA: Metropolitan Atlanta Rapid Transit Authority (FTA4)

MASPS: Minimum Aviation System Performance Standards (FAA17)

MASS: Maintenance Automation System Software (FAA20)

Mass Transit: Another name for public transportation. (APTA1)

Mass Transportation: Another name for public transportation. (APTA1)

Mass Transportation Agency: An agency authorized to transport people by bus, rail, or other conveyance, either publicly or privately owned, and providing to the public general or special service (but not including school, charter or sightseeing service) on a regular basis. (FTA1)

MATCU: Military Air Traffic Coordinating Unit (MTMC1)

Material Handling: Short-distance movement of goods within a storage area. (MARAD1)

Material Handling Equipment: Forklift trucks, platform trucks, warehousing industrial cranes, straddle carrier trucks, pallet trucks, platform trucks, warehousing trailers, conveyer systems, and others, used in storage and handling operations. (MARAD1)

MATES: Mobilization & Training Equipment Site (MTMC1)

MAWDT: Monthly Average Weekday Traffic (FHWA19)

MAWET: Monthly Average Weekend Traffic (FHWA19)


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