Aviation Maintenance Terms beginning with M

Mach number

The ratio of true airspeed to the speed of sound.

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Main rotor

The rotor that supplies the principal lift to a rotorcraft.

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Maintenance

Inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance. (1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or (2) That is not done according to accepted practices or cannot be done by elementary operations.

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Major repair

A repair: (1) That, if improperly done, might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or (2) That is not done according to accepted practices or cannot be done by elementary operations.

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Manifold pressure

Absolute pressure as measured at the appropriate point in the induction system and usually expressed in inches of mercury.

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Maximum engine overtorque

As it applies to turbopropeller and turboshaft engines incorporating free power turbines for all ratings except one engine inoperative (OEI) ratings of two minutes or less, is the maximum torque of the free power turbine rotor assembly, the inadvertent occurrence of which, for periods of up to 20 seconds, will not require rejection of the engine from service, or any maintenance action other than to correct the cause.

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Maximum speed for stability characteristics, VFC /MFC

A speed that may not be less than a speed midway between maximum operating limit speed (VMO/MMO) and demonstrated flight diving speed (VDF/MDF), except that, for altitudes where the Mach number is the limiting factor, MFC need not exceed the Mach number at which effective speed warning occurs.

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Minor alteration

An alteration other than a major alteration.

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Minor repair

A repair other than a major repair.

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