Weight and Balance Extreme Conditions

in Aircraft Weight and Balance

A weight and balance extreme condition check, sometimes called an adverse condition check, involves loading the aircraft in as nose heavy or tail heavy a condition as possible, and seeing if the center of gravity falls outside the allowable limits. This check is done with pencil and paper. In other words, the aircraft is not actually loaded in an adverse way and an attempt made to fly it.

On what is called a forward extreme condition check, all useful load items in front of the forward CG limit are loaded, and all useful load items behind the forward CG limit are left empty. So if there are two seats and a baggage  compartment located in front of the forward CG limit, two people weighing 170 lb each will be put in the seats, and the maximum allowable baggage will be put in the baggage compartment. Any seat or baggage compartment located behind the forward CG limit will be left empty. If the fuel is located behind the forward CG limit, minimum fuel will be shown in the tank. Minimum fuel is calculated by dividing the engine’s METO horsepower by 2.

On an aft extreme condition check, all useful load items behind the aft CG limit are loaded, and all useful load items in front of the aft CG limit are left empty. Even though the pilot’s seat will be located in front of the aft CG limit, the pilot’s seat cannot be left empty. If the fuel tank is located forward of the aft CG limit, minimum fuel will be shown.

Example Forward and Aft Extreme Condition Checks

Figure 4-24. Example airplane for extreme condition checks.

Figure 4-24. Example airplane for extreme condition checks.

Using the stick airplane in Figure 4-24 as an example, adverse forward and aft checks will be calculated. Some of the data for the airplane is shown in the figure, such as seat, baggage, and fuel information. The center of gravity limits are shown, with arrows pointing in the direction where maximum and minimum weights will be loaded. On the forward check, any useful load item located in front of 89″ will be loaded, and anything behind that location will be left empty. On the aft check, maximum weight will be added behind 99″ and minimum weight in front of that location. For either of the checks, if fuel is not located in a maximum weight location, minimum fuel must be accounted for. Notice that the front seats show a location of 82″ to 88″, meaning they are adjustable fore and aft. In a forward check, the pilot’s seat will be shown at 82″, and in the aft check it will be at 88″. Additional specifications for
the airplane shown in Figure 4-24 are as follows:

• Airplane Empty Weight: 1,850 lb
• Empty Weight CG: +92.45″
• CG Limits: +89″ to +99″
• Maximum Weight: 3,200 lb
• Fuel Capacity: 45 gal at +95″ (44 usable) — 40 gal at +102″ (39 usable)

In evaluating the two extreme condition checks, the following key points should be recognized.

  • The total arm is the airplane center of gravity, and is found by dividing the total moment by the total weight.
  • For the forward check, the only thing loaded behind the forward limit was minimum fuel.
  • For the forward check, the pilot and passenger seats were shown at the forward position of 82″.
  • For the forward check, the CG was within limits, so the airplane could be flown this way.
  • For the aft check, the only thing loaded in front of the aft limit was the pilot, at an arm of 88″.
  • For the aft check, the fuel tank at 102″ was filled, which more than accounted for the required minimum fuel.
  • For the aft check, the CG was out of limits by 0.6″, so the airplane should not be flown this way.
Figure 4-25. Center of gravity extreme condition checks.

Figure 4-25. Center of gravity extreme condition checks.