Payloads – Mass Definitions

Commonly, “weight” and “mass” are used interchangeably, but they are specific terms:

• Mass (m): The amount of “matter” that is in an object
• Weight (W): The force exerted by a mass due to gravity

Usable fuel is the fuel on board an aircraft that can actually be used by its engines.

The small amount of fuel that cannot be drained from the tanks is the unusable fuel.

For calculation of range, usable fuel is used. For weight and balance total fuel (usable + unusable) is used.

For a battery, this is like saying that we can only deplete the voltage to a certain level, where we must still leave a little power in the battery to avoid damaging it. For weight and balance, total battery mass is used.

Dry Operating Mass (DOM)

Dry Operating Mass (DOM) is the total mass of the aeroplane ready for a specific type of operation excluding usable fuel and traffic load. Mass includes items such as crew and crew baggage.

Operating Mass (OM)

Operating Mass (OM) is the DOM plus take-off fuel but without traffic load.

Basic Operating Weight (BOW)

Basic Operating Weight (BOW) is the total weight of the aircraft, including crew, ready for flight, but without payload or fuel (sometimes excludes the crew).

Includes all fixed ballast, unusable fuel, normal operating level of oil and total quantity of hydraulic fluid (transport aircraft only)

Zero-fuel weight (ZFW)

Zero-fuel weight (ZFW) is the total weight of the airplane and all its contents (including unusable fuel), but excluding the total weight of the usable fuel on board.

As a flight progresses and fuel is consumed, the total weight of the airplane reduces, but the ZFW remains constant.

Manufacturer’s Empty Weight (MEW)

Also called Manufacturer’s Weight Empty (MWE) or Licensed Empty Weight (LEW)

It is the weight of the aircraft “as built” and includes the weight of the structure, power plant, furnishings, installations, systems and other equipment that are considered an integral part of an aircraft.

This excludes any baggage, passengers, or usable fuel.

Aircraft Gross Weight

It is the total aircraft weight at any moment during the flight or ground operation. This decreases during flight due to fuel and oil consumption.

Maximum Ramp Weight (MRW)

Also called Maximum Taxi Weight (MTW)

It is the maximum weight authorized for manoeuvring (taxiing or towing) an aircraft on the ground.

Maximum Take-Off Weight (MTOW)

Maximum takeoff weight (MTOW) of an aircraft is the maximum weight at which the pilot is allowed to attempt to take off, due to structural or other limits.

It is also known as:

• Maximum gross take-off weight (MGTOW)
• Maximum takeoff mass (MTOM)

MTOW of an aircraft is fixed and does not vary with altitude, air temperature, or the length of the runway to be used for take-off or landing.

• MTOW is usually specified in units of kilograms or pounds.
• MTOW is the heaviest weight at which the aircraft has been shown to meet all the airworthiness requirements applicable to it.

Maximum Landing Weight (MLW)

Maximum landing weight (MLW) is the maximum aircraft gross weight due to design or operational limitations at which an aircraft is permitted to land.

The MLW is set in order to ensure safe landings; if an aircraft weighs too heavy during touchdown, it may suffer structural damage or even break apart upon landing.

Note: The MTOW is almost always higher than the maximum landing weight, so that an aircraft can weigh less upon landing due to burning fuel during the flight.

Maximum Zero Fuel Weight (MLW)

Maximum Zero Fuel Weight (MZFW) is the maximum weight allowed before usable fuel and other specified usable agent (engine injection fluid, and other consumable propulsion agents) are loaded.

BOW (Basic Operating Weight)

Dry Operating Weight (DOW) = BOW + crew, bags, catering and spares

Operating Weight (OW) = DOW + take-off fuel

Zero Fuel Weight (ZFW) = DOW + payload/passenger load

Zero Fuel Weight (ZFW) = TOW – take-off fuel

Take-off Weight (TOW) = ZFW + take-off fuel

Taxi Weight = TOW + taxi fuel

Landing Weight (LDW) = TOW – fuel consumed en-route