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lowest level of the sea. Mean values are used when measuring from a reference that moves, or changes,
between specific limits.
mean aerodynamic chord. See MAC.
mean camber. A line that is drawn midway between the upper and lower camber of an airfoil section. The
mean camber determines the aerodynamic characteristics of the airfoil.
mean sea level. See MSL.
mean solar day. The time it takes the earth to rotate about its axis, with respect to the mean location of the
sun. The length of a mean solar day is 24 hours, 3 minutes, and 56.555 seconds.
measured ceiling (meteorology). A ceiling classification applied when the ceiling value has been
determined by instruments or the known heights of unobscured portions of objects other than natural
landmarks.
mechanic. A person skilled in repairing mechanical devices. The Federal Aviation Administration issues a
license for aircraft mechanics, and there were two ratings used with this license: airframe and powerplant.
The term mechanic is scheduled to be replaced by technician, and the Mechanic Certificate replaced by the
Aviation Maintenance Technician Certificate by the proposed 14 CFR Part 66, Aviation Maintenance
Personnel.
mechanical advantage. The increase in force or speed produced by a mechanical device, such as the lever,
pulley, gears, or hydraulic cylinder. These devices increase speed or force, but they cannot produce work.
The force needed to lift a weight may be reduced, or the speed at which an object moves may be changed.
But if mechanical losses are discounted, the amount of work (force times distance) taken from the device is
the same as the amount of work put into it.
mechanical blockage thrust reverser (gas turbine engine component). A type of thrust reverser that
uses a pair of clamshell doors set into the tail cone of the engine to deflect the exhaust gases forward when
the pilot wants to slow the aircraft.
mechanical efficiency (reciprocating engines). The ratio of the amount of brake horsepower delivered to
the output shaft of a reciprocating engine to the amount of indicated horsepower produced in the cylinders
of the engine.
Mechanic Certificate. A certificate issued under 14 CFR Part 65, Certification: Airmen other than Flight
Crewmembers, to a person who demonstrates the required experience, knowledge, and skills. This
certificate must be accompanied by either an Airframe or Powerplant rating or both.
The proposed 14 CFR Part 66, Certification, Aviation Maintenance Personnel, replaces the
Mechanic Certificate and ratings with an Aviation Maintenance Technician Certificate with an Aircraft
rating or an Aviation Maintenance Technician (Transport) Certificate with an Aircraft rating.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 378
This proposed regulation also makes provisions for an Aircraft Maintenance Instructor rating to be
applied to either the AMT or AMT(T) Certificate.
median (mathematics). The number, in a series, that has as many numbers below it as there are above it.
In the series of numbers 1, 2, 3, 4, 5, 6, 7 the median is 4. There are three numbers below 4 and three
numbers above it.
medical certificate. 14 CFR Part 1: “Acceptable evidence of physical fitness in a form prescribed by the
Administrator.”
medium-bypass turbofan engine. A turbofan engine with a bypass ratio of between 2:1 and 4:1. This
means that the fan moves two to four times as much air as the core engine.
medium frequency (radio transmission frequency). The portion of the band of frequencies of
electromagnetic radiation between 300 kilohertz and 3 megahertz. Commercial radio broadcasting uses the
medium frequency band.
medium-scale integration (MSI). An integrated circuit chip having between 10 and 100 gates or
gate-equivalent circuits.
mega (M). The metric prefix that means one million, 1,000,000, or 106.
Megger. The registered trade name for a high-voltage, high-range ohmmeter. A Megger has a built-in,
hand-turned generator, to produce the high voltage needed to measure the resistance. Meggers are used to
measure insulation resistance and the resistance between components and electrical ground.
megohmmeter. An instrument used to measure very high values of resistance such as found in materials
normally considered to be insulators. Megohmmeters use a high voltage to force current through the
material and a sensitive indicator to measure the extremely small current that results.
MEK (methyl-ethyl-ketone). A volatile organic chemical solvent that is soluble in water and is used as a
solvent for vinyl and nitrocellulose films. MEK is an efficient solvent for removing oily contaminants from
ignition system components and for cleaning and preparing surfaces for priming or painting. MEK’s
　
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