Next to a good preflight plan and weather report is a thorough Weight & Balance calculation. Weight & balance is a matter of serious concern to all pilots as well as many other people involved in the flight. The pilot has to personally assume the responsibility (and by law) because he has control over both the loading and fuel management, the two variable factors which can change both total weight & balance. This information is available to the pilot in the form of aircraft records, operating handbooks and placards in baggage compartments and or fuel caps. The owner of the aircraft has the responsibility to make sure that up to date information is available to the pilot.

To understand what is going on with Weight & Balance calculations we need to establish some definitions. Using these terms and definitions we al speak the same language and there is no confusion. Therefore we complied a list of the most common terms used in weight & balance calculations.

Weight & Balance Terminology

MTOW or MAUW
The maximum weight allowable for the aircraft at the beginning of the takeoff run. This value is given in the Aircraft Flight Manual or Pilots Operating Handbook of the aircraft in the limitations section. Some aircraft have a higher permitted weight for takeoff than they do for landing. Also some aircraft have a socalled 'ramp weight' which is higher than MTOW or MAUW, the difference is fuel burned off by taxi, see below.

Basic Empty Weight
The weight of the aircraft, including aircraft, engine(s), all installed equipment, full operating oil and unusable fuel in all tanks. Also found in the Aircraft Flight Manual or Pilots Operating Handbook of the aircraft in the limitations section, it is also noted on the basic weight & balance sheet of the aircraft. It is expressed in pounds (lbs) or kilograms (kg).

Basic Operating Weight
This is the Basic Empty Weight plus pilot(s) and cabin crew (if any), crews baggage, food, water. Thus the total load minus payload and fuel.

Payload
The commercial load, thus the passengers, baggage, cargo from which revenue is generated.

Zero Fuel Weight
This is Basic Operating Weight plus Payload.

Fuel Weight
One liter AVgas weighs 0.72 kg, thus its specific gravity is .72 (at ISA atmosphere standards) or put differently 6 lbs/gallon (US). AVtur (Aviation Turbine Fuel) is in the range of .79 to .83 and on average .81, or 6.76 lbs/gallon (US).

Ramp Weight
The Zero Fuel Weight of the aircraft plus fuel needed for the anticipated flight. Sometimes higher than Maximum Take-off Weight because of startup, taxi and runup fuel. It is not always specified for light aircraft.

Gross Weight
The total weight of the aircraft at any particular time. Thus Basic Empty Weight plus Pilot, Crew and their baggage plus payload (passengers and cargo) plus fuel load. Gross Weight may not exceed the maximum weight permissable for any given manoeuvre at any time.

Maximum Landing Weight
This is the maximum allowable weight of the aircraft for landing, it is a structural limit. Light aircraft usually have the same weight for landing and takeoff, but many larger aircraft must burn off fuel (or dump it) before the actual gross weight is below Maximum Landing Weight. Important in case of a immediate return after takeoff.

Weight and Mass
Snippets From Wikipedia: In the physical sciences, weight is a measurement of the gravitational force acting on an object. Near the surface of the Earth, the acceleration due to gravity is approximately constant; this means that an object's weight is roughly proportional to its mass. In modern scientific usage, weight and mass are fundamentally different quantities: mass is an intrinsic property of matter, whereas weight is a force that results from the action of gravity on matter: it measures how strongly gravity pulls on that matter.
To convert between weight (force) and mass we use Newton's second law, F = ma (force = mass × acceleration). Here, F is the force (weight) due to gravity, m is the mass of the object in question, and a is the acceleration due to gravity, on Earth approximately 9.8 m/s² or 32.2 ft/s². In this context the same equation is often written as W = mg, with W standing for weight, and g for the acceleration due to gravity.

Datum
An imaginairy vertical line, specified by the designer of the aircraft, from which all horizontal C of G measurement are made. In most cases, the datum is located near the aircraft nose. It is usually the firewall. The datum for a particular aircraft is stated in the Pilot Operating Handbook or the Aircraft Flight Manual.

Arm or Station
This is the horizontal distance from the datum to the C of G of the aircraft or any item in the aircraft. A positive sign indicates measurement aft of the datum. You will find these values in the Aircraft Flight Manual or Pilots Operating Handbook of the aircraft and they can be expressed in inches, centimeters or meters.

Moment
Based on Newtons second law: F = ma (force = mass × acceleration). The weight of an item multiplied by the arm of its position. In engine terminology this is called torque.

Moment of a force
This is the turning effect about a given point and it depends on two things: the magnitude of the force (weight) and its distance (arm). If the force is measured in kilograms and the arm in meters then the moment is expressed in kilogram/meters.
Remember that in aircraft center of gravity calculations all moments that tend to result in a nose-up rotation about the selected datum are positive and vice versa.

Center of Gravity
This is the point about which an aircraft would balance if suspended on this point. It is the sum of all moments in the W & B calculations or put another way: the pivotal point about which the nose heavy and the tail heavy moments are of equal magnitude.

Center of Gravity Limits
Very important: these are the forward and aft limits in which the C of G must fall if the aircraft is to be operated safely and in stable controlled flight. These points are specified in the limitations section of the Aircraft Flight Manual or Pilots Operating Handbook of the aircraft and are determined by the designer of the aircraft.