Effects of Shifting Cargo From One Hold to  Another When cargo is shifted from one cargo hold to another, the CG  changes, but the total weight of the aircraft remains the same. For example, use the following data: To determine the change in CG (ΔCG) caused by shifting  2,500 pounds of cargo from the forward cargo hold to the  aft cargo hold, use the formula in  Figure 9-20 . Some AFMs locate the CG relative to an index point rather  than the datum or the MAC. An index point is a location  specified by the aircraft manufacturer from which arms used  in weight and balance computations are measured. Arms  measured from the index point are called index arms, and  objects ahead of the index point have negative index arms,  while those behind the index point have positive index arms.  Since the weight was shifted aft, the CG moved aft and the  CG change is positive. If the shift were forward, the CG  change would be negative. Use the same data as in the previous example, except for  these changes: The weight was shifted 372.8 inches (–227.9 + Δ = +144.9,  Δ =372.8). The change in CG can be calculated by using this formula  found in  Figure 9-24 . Before the cargo was shifted, the CG was located at station  580.97, which is 22.5 percent of MAC. The CG moved aft  10.36 inches, so the new CG is found using the formula from  Figure 9-21 . Convert the location of the CG in inches aft of the datum to  percent MAC by using the formula in  Figure 9-22 .  The new CG in percent MAC caused by shifting the cargo is  the sum of the old CG plus the change in CG.  [Figure 9-23] 9-8 Figure 9-24.  Determining the change in CG caused by shifting  2,500 pounds of cargo. Figure 9-21.  Determining the new CG after shifting cargo weight. Figure 9-23.  Determining the new CG in percent MAC. Figure 9-22.  Converting the location of CG to percent MAC. Loaded weight ................................................ 90,000 lb Loaded CG............. station 580.97 (22.5 percent MAC) Forward cargo hold centroid........................ station 352 Aft cargo hold centroid............................. station 724.9 MAC .................................................................. 141.5 in LEMAC ....................................................... station 549 ( ) CG % MAC = × 100 CG inches MAC ( ) = × 100 10.36 141.5 = 7.32% MAC New CG % MAC = Old CG – CG = 29.82% MAC = 22.5% + 7.32% CG = Weight shifted × Distance shifted Total weight = 2,500 × (724.9 – 352) 90,000 = 2,500 × 372.9 90,000 = 10.36 inches New CG = Old CG – CG = 591.33 inches = 580.97 + 10.36 CG = × 100 Weight shifted × Distance shifted Total weight = 2,500 × (227.9 + 144.9) 90,000 = 2,500 × 372.8 90,000 = 10.36 inches Figure 9-20.  Calculating the change in CG, using index arms. Loaded CG.......................... index arm of 0.97, which is  22.5 percent of MAC Index point................................... fuselage station 580.0 Forward cargo hold centroid............... –227.9 index arm Aft cargo hold centroid.......................+144.9 index arm MAC .................................................................. 141.5 in LEMAC .............................................. –30.87 index arm