Empty weight – has unusable fuel, unusable oil, airframe, engine fixed equipments.
Basic Empty weight – has unusable fuel, full oil, airframe, engine & fixed equipment.
Operating weight – Basic empty weight & Pilots, crews, special equipments etc. but does not include Pay load & Usable fuel.
Zero fuel weight – Operating weight & payload (but does not include usable fuel) Any weight added above this should be in the form of fuel.
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It has Basic Empty weight + Pilots + Crew + Passenger + Baggage & cargo + Unusable fuel in the tanks.
Gross Weight is Basic Empty weight + Pilots + crew + Payload + Total fuel.
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Useful load is the difference between the Maximum Ramp weight & Basic Empty weight.