Glossary of Terms

	Title	Definition
	Localizer	The horizontal guidance portion of an Instrument Landing System. Indicates to the pilot whether he is to the left of, to the right of, or on course.
	LOG	Localised VHF radio beacon providing accurate horizontal guidance.
	Lowest Safe Altitude (LSA)	Designated minimum altitude for particular air route, providing minimum of 1,000 feet clearance above underlying terrain.
	MAC	Mean Aerodynamic Chord.
	Mach number	Figure expressing relationship between true airspeed of aircraft and speed of sound.
	Maintainability	The ability of an item to be retained in or restored to specified condition when maintenance is performed by personnel having specified skill levels, using prescribed procedures, resources and equipment at each prescribed level of maintenance and repair.
	Malfunction	Fail to operate in the normal or usual manner. Any anomaly which results in system deviation.
	Mayday (repeated three times)	Radio telephony version of former morse code "SOS" distress call. Derived from the French "m'aidez" - "help me".
	Mean Time Between Failures (MTBF)	Indicates mean life of repairable items. As the reciprocal of failure rate, MTBF is an alternative for describing the random failure portion of the bath-tub curve) MTBF is the "average" time between failures, the reciprocal of the failure rate in the special case when failure rate is constant. Calculations of MTBF assume that a system is "renewed", i.e. fixed, after each failure, and then returned to service immediately after failure. MTBF= (Number of flight hours x units installed per aircraf)/(Number of shop confirmed failures during that period)
	Mean Time To Failure (MTTF)	Indicates mean life of non-repairable items.
	MEMS	Maintenance Error Management Systems
	Methodology	A particular procedure or set of procedures.
	Mishap	An unplanned event or series of events resulting in death, injury, occupational illness, damage to or loss of equipment or property, or damage to the environment [MIL-STD-882D].
	Mishap Risk	An expression of the impact and possibility of a mishap in terms of potential mishap severity and probability of occurrence [MIL-STD-882D].
	Mitigation	Any downstream circumstances or functions that reduces the probability of a malfunction escalating to an accident

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