Zero Fuel Weight (ZFW) is the maximum permissible weight of an airplane with no disposable fuel or oil. In simple terms, zero fuel weight is the most an airplane can weigh when loaded with passengers and cargo with no usable fuel or oil onboard. The zero fuel weight figure should be in either the airplane type certificate data sheet or the approved Airplane Flight Manual.
Zero Fuel Weight is set due to the flexing of wings in turbulence, which applies bending loads to the wing roots. The bending loads increase significantly as weight in the fuselage increases.
All weight over and above the Maximum Zero Fuel Weight must be in the form of fuel in the wings.
Here is an example. Consider a plane with the following characteristics:
1. MTOW of 14,800 lbs
2. an Empty Weight of 9500 lbs
3. A fuel capacity of 4800 lbs
4. A ZFW of 11,300 lbs
This plane can hold 5300 lbs of "Stuff" - Fuel or cargo. However, the ZFW limits the amount of cargo that can put on. The pilot can only put on 1800 lbs of cargo (11,300 -9500), even though there is a 5300 pound loading capability including fuel. So, because of ZFW, the pilot will be cargo limited.
ZFW is a published limitation. If no ZFW is published, the aircraft has no ZFW limit.