TM 1-1510-224-10 can be established.   Maximum Weight The largest weight allowed by design, structural, Service Ceiling The altitude at which the performance or other limitations. maximum rate of climb of 100 feet per minute can be Maximum Zero Fuel Any weight above the value attained for existing aircraft Weight must be loaded as fuel. weight. Moment A measure of the rotational Takeoff Weight The weight of the aircraft at tendency of a weight, about a lift-off from the runway. specified line, mathematically equal to the product of the B-6.  WEIGHT AND BALANCE TERMINOLOGY. weight and the arm. Approved Loading -Those combinations of air- Standard Weights corresponding to the Envelope craft weight and center of aircraft as offered with seat- gravity which define the limits ing and interior, avionics, beyond which loading is accessories, fixed ballast and not approved. other equipment specified by the manufacturer as composing Arm The distance from the center a standard aircraft of gravity of an object to a line about which moments are Station The longitudinal distance to be computed. from some point to the zero Basic Empty Weight The aircraft weight with fixed datum or zero fuselage ballast, unusable fuel, engine station. oil, engine coolant, hydraulic Takeoff Weight The weight of the aircraft at fluid, and in other respects as liftoff. required by applicable regulatory standards.   Unusable Fuel The fuel remaining after consumption of usable fuel. Center-of-Gravity A point at which the weight of an object may be considered Usable Fuel That portion of the total fuel concentrated for weight which is available for and balance purposes. consumption as determined in accordance with applicable CG Limits CG limits are the extremes of regulatory standards. movement which the CG can Useful Load have without making the air- The difference between the craft unsafe to fly.  The CG of aircraft ramp weight and the loaded aircraft must be basic empty weight. within these limits at takeoff, in the air, and on landing. B-7.  MISCELLANEOUS ABBREVIATIONS. Datum A vertical plane perpendicular A/A Air to air to the aircraft longitudinal AAA Anti-aircraft artillery axis from which fore and aft (usually aft) measurements AC Advisory circular, alternating are made for weight and current balance purposes. ACCEL Accelerometer, acceleration Engine Oil That portion of the engine oil which can be drained from ACS Avionics control system which can be drained from the engine. ACT Active Landing Weight The weight of the aircraft at A/D Analog to digital landing touchdown. B-4