<< Back
  

Maximum Weight Limits

"Portions of this work are Copyright (c) 2009 Jeppesen.  
Used By Permission"

 




Aircraft Weights
The weight and distribution of items carried in an airplane has tremendous effect on aircraft performance and aerodynamic stability. Before an aircraft can safely commence flight the pilot should consider whether the loading conditions of the airplane are within allowable limits. These limits are established by the aircraft manufacturer and should have been demonstrated to the FAA in order to meet airworthiness certification requirements. If the aircraft is loaded within these limits, it will be stable and controllable during the entire flight envelope. On the other hand, if the aircraft is improperly loaded and a flight would be commenced, safety and performance will be compromised in many ways.
Maximum Weight Limitations
In order to provide safe flight operations, the pilot must maintain the total, or gross, weight of an airplane at or below maximum limits. These maximum weights are primarily established to maintain structural integrity of the airframe up to the limit load factors during all phases of flight. Small, low-powered aircraft are usually restricted by a maximum weight limit specified as maximum certificated weight, maximum gross weight or simply maximum weight. Larger aircraft, however, are restricted by maximum weight limits designated for various stages of flight and ground operations. These weights are commonly referred to as the Maximum Zero Fuel Weight (MZFW), Maximum Ramp Weight, Maximum Take-off Weight (MTOW) and Maximum Landing Weight (MLAW).

Maximum Zero Fuel Weight
Some, and almost all commercial aircraft, have a Maximum Zero Fuel Weight, which is the maximum amount of weight of the aircraft without usable fuel. In order to determine the MZFW, you can simply extract the total amount of usable fuel on board from the aircraft weight. If, for some reason, the actual zero fuel weight is higher than the MZFW, items, other than fuel, must be reduced in order to reduce the total load. The reason why the MZFW is established is to determine the maximum weight that can be carried in the aircraft fuselage. Excessive loading could result into the wings flexing too far upward when generating sufficient lift required to keep the aircraft airborne.

Maximum Ramp Weight
The Maximum Ramp Weight is specified as the maximum amount the aircraft can weight on the ramp or during taxi. Obviously, this maximum weight is higher than the maximum take-off weight in order to provide an allowance for the amount of fuel used from engine start until the take-off roll (called taxi fuel). In some cases, the manufacturer uses the term Maximum Taxi Weight, however, these terms represent the same limitation.

Actual Ramp/Taxi Wt.
Actual Zero Fuel Weight
+
Block Fuel
=
Actual Ramp/Taxi Weight


Maximum Take-off Weight
The Maximum Take-off Weight is determined as the weight of the aircraft as the brakes are released at the beginning of the runway to start the take-off run. Both for the MTOW and MLAW, the manufacturer determined that the total weight of the aircraft permitted for flight may cause structural damage to the airframe as load limits are exceeded during take-off or landing. It is therefore important to make sure the fuel consumption during flight is sufficient to reduce total weight of the aircraft to the MLAW prior to landing.

Actual Take-off Weight
Actual Ramp/Taxi Weight
-
Taxi Fuel
=
Actual Take-off Weight

Maximum Landing Weight
The Maximum Landing Weight is, as already pointed out earlier, related to the maximum amount the aircraft may weigh at touchdown. This restriction is based on the strength of the landing gear and overall structural fuselage integrity. For weight and balance reasons, the lowest of these four is used to establish the maximum allowable payload.


Actual Landing Weight
Actual Take-off Weight
-
Trip Fuel
=
Actual Landing Weight