machine-sewn seams (aircraft fabric covering). Seams in aircraft fabric made with a sewing machine. French fell, folded fell, and plain overlap are the seams most generally used.

machining. The process of removing material by turning, planing, shaping, milling, or otherwise cutting with machine-operated tools. Lathes, milling machines, shapers, and planers are the most commonly used machine tools.
machinist. A person skilled in the use of such metalworking machine tools as lathes, shapers, planers, and milling machines.
Machmeter. A flight instrument that indicates the flight Mach number of an aircraft. The mechanism inside a Machmeter includes a bellows that measures the difference between pitot pressure and static pressure. It also contains an aneroid that modifies the output of the differential pressure bellows to correct for the changes in altitude.
Mach number. A measurement of speed based on the ratio of the speed of the aircraft to the speed of sound under the same atmospheric conditions. An airplane flying at Mach 1 is flying at the speed of sound. 14 CFR Part 1: “The ratio of true airspeed to the speed of sound.”
Mach technique (ICAO). 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 enroute phase of flight. The principal objective is to achieve improved utilization of the airspace and to ensure that separation between successive aircraft does not decrease below the established minimums.
Mach tuck (aerodynamics). A flight condition that can occur when operating a swept wing airplane in the transonic speed range. Under certain conditions a shock wave forms in the root portion of the wing and causes the air behind it to separate. This shock-induced separation causes the center of lift to move aft. At the same time, the disturbed air causes the horizontal stabilizer to lose some of its effectiveness. The airplane develops a nose-down pitch, or tucks under. See shock stall.
mackerel sky (meteorology). A condition of cloud coverage of the sky consisting of rows of altocumulus or cirrocumulus clouds. These clouds look like the pattern of scales on a mackerel fish.
magamp. See magnetic amplifier.
magnesium. A light, silvery-white, malleable, ductile, metallic chemical element. Magnesium’s symbol is Mg, its atomic number is 12, and its atomic weight is 24.312. Magnesium burns with an intense white light, and because of this, it is used for making flares.
Magnesium’s light weight makes it useful as a structural material, but it has disadvantages. It corrodes easily, and vibration causes it to crack.
Magnesyn. The registered trade name for a remote indicating system, used in certain aircraft instruments. A Magnesyn transmitter consists of a permanent-magnet rotor, free to rotate inside a toroidal coil. The magnet is rotated by the physical movement being measured. The indicator contains a small permanent magnet on a shaft, free to rotate inside a toroidal coil. A pointer is also mounted on the shaft.