Magnetic flux.  Lines of magnetic force that are assumed to  leave a magnet at its north end and return to its south end.  Lines of flux tend to be as short as possible and cannot cross  each other. Liquid cooling.  The removal of unwanted heat from an  aircraft engine by transferring the heat into a liquid and  then passing the heated liquid through a liquid-to-air heat  exchanger (radiator) to transfer the heat into the ambient air. Longitudinal magnetism.  A method of magnetizing through a  solenoid, or coil, that encircles the part so the lines of magnetic  flux pass lengthwise through the part. Longitudinal magnetism  makes it possible to detect faults that extend across the part. Magnetic particle inspection.  A method of non-destructive  inspection for ferrous metal components. The part being  inspected is magnetized and then flooded with a solution of  iron oxide suspended in a light oil, much like kerosene. Any  flaw, either on the surface or just below the surface, forms a  north and south pole, and the iron oxide attracted to these poles  helps locate the flaw. The iron oxide is normally treated with a  fluorescent dye, and the inspection is conducted in a darkened  booth. When an ultraviolet light (black light) is shone on the  part, the treated iron oxide shows up as a brilliant line. Low bypass ratio engine.  A turbofan engine whose bypass  ratio is less than 2:1. Low-pressure compressor.  The first-stage compressor in a  dual-spool gas turbine engine. The low-pressure compressor  is called the N1 compressor and its speed is not governed.  It seeks its own best speed as the atmospheric conditions  change so it can furnish a relatively constant mass of air to  the inlet of the second-stage compressor. Major alteration.  An alteration not listed in the aircraft, aircraft  engine, or propeller specifications that might appreciably affect  weight, balance, structural strength, powerplant operation,  flight characteristics, or other qualities affecting airworthiness;  an alteration not done according to accepted practices, or one  that cannot be done by elementary operations. Low unmetered fuel pressure.  Pressure in a Teledyne- Continental fuel injector pump that is adjusted by the relief  valve. LRU.  Line replaceable unit. Aircraft components designed  to be replaced as a unit while the aircraft is on the flight line. Major overhaul.  The disassembly, cleaning, and inspection  of an engine and the repair and replacement of all parts that  do not meet the manufacturer’s specification. M&D (Malfunction and Defect) report.  A small postcard- like form (FAA Form 8330) used by repair stations,  maintenance shops, and technicians to report an unacceptable  condition to the FAA. Information on these forms provides  the basis for the General Airworthiness Alerts and subsequent  Airworthiness Directives. Major repair.  A repair to a component that if improperly  done might appreciably affect weight, balance, structural  strength, performance, powerplant operation, flight  characteristics, or other qualities affecting airworthiness; a  repair not done according to accepted practices, or one that  cannot be done by elementary operations. Mach number.  The ratio of the speed of an object through  the air to the speed of sound under the same atmospheric  conditions. An object traveling at the speed of sound is  traveling at Mach one (M1.0). Mandrel.  A precision steel bar on which a propeller is  mounted for balancing. The mandrel is placed across two  perfectly level knife-edge plates, and the propeller is allowed  to rotate until it stops with its heavy point at the bottom. Manifold pressure.  The absolute pressure of the air inside  the induction system of a reciprocating engine. Magnesyn system.  The registered trade name of a remote  indicating instrument system. A Magnesyn system uses a  permanent magnet as its rotor and a toroidal coil excited by  400-hertz AC as its stator. A small magnet in the center of  the indicator coil follows the movement of a larger magnet  in the transmitter coil. Manifold valve.  See flow divider (reciprocating engine). MAP. Manifold absolute pressure.  The absolute pressure  that exists within the induction system of a reciprocating  engine. It is the MAP that forces air into the cylinders of the  engine. MAP is commonly called manifold pressure. Magnetic field.  The invisible, but measurable, force  surrounding a permanent magnet or current-carrying  conductor. This field is produced when the orbital axes of  the electrons of the atoms in the material are all in alignment. G-17