Figure 7-5.  Weight and moment index changes caused by a typical alteration or repair. Figure 7-4.  Weight, arm, and moment changes caused by typical alteration or repair. 7-5 Weight Changes Caused by a Repair or  Alteration Computations Using Weight, Arm, and Moment The first step in the weight and balance computation is to  make a chart like the one in  Figure 7-4 , listing all of the  items that are involved. The new center of gravity (CG) of  36.4 inches aft of the datum is determined by dividing the  new moment by the new weight. Computations Using Weight and Moment Indexes If the weight and balance data uses moment indexes rather  than arms and moments, this same alteration can be computed  using a chart such as the one in  Figure 7-5 . Subtract the  weight and moment indexes of all the removed equipment  from the empty weight and moment index of the airplane.  Add the weight and moment indexes of all equipment  installed to determine the total weight and the total moment  index. To determine the position of the new CG in inches  aft of the datum, multiply the total moment index by 100 to  get the moment, and divide this by the total weight to get  the new CG. A typical alteration might consist of removing two pieces  of radio equipment from the instrument panel and a power  supply that was located in the baggage compartment behind  the rear seat. In this example, these two pieces are replaced  with a single lightweight, self-contained radio. At the  same time, an old emergency locator transmitter (ELT) is  removed from its mount near the tail, and a lighter weight  unit is installed. A passenger seat is installed in the baggage  compartment. The weight and balance revision sheet should clearly show  the revised empty weight, empty weight arm and/or moment  index, and the new useful load. An example of these entries  can be found at the bottom of  Figure 7-3 . Item Weight (lb) Arm (in) Moment (lb-in) New CG 67,723.6 −192.8 −874.0 −432.0 +122.6 +229.5 +2,037.0 68,613.9 +36.4 Airplane Radio removed Power supply removed ELT removed Radio installed ELT installed Passenger seat installed Total 1,876.0 −12.2 −9.2 −3.2 +8.4 +1.7 +21.0 1,882.5 36.1 15.8 95.0 135.0 14.6 135.0 97.0 x = Item Weight (lb) Moment indexes (lb-in/100) New CG (inches from datum) +677.2 −1.93 −8.74 −4.32 +1.23 +2.29 +20.37 +686.1 +36.4 Airplane Radio removed Power supply removed ELT removed Radio installed ELT installed Passenger seat installed Total 1,876.0 −12.2 −9.2 −3.2 +8.4 +1.7 +21.0 1,882.5