9-5 MAC-based CG envelope (e.g., canard equipped airplane),  whenever the cumulative change in the CG position exceeds  one-half of 1 percent (0.5 percent) of the total CG range, the  weight and balance should be reestablished.  When reestablishing the aircraft OEW between reweighing  periods, the weight changes may be computed provided the  weight and CG location of the modifications are known;  otherwise, the aircraft must be reweighed.  An operator may choose to use one weight for a fleet or group  of aircraft if the weight and CG of each aircraft is within the  limits stated above for establishment of OEW. When the  cumulative changes to an aircraft weight and balance log  exceed the weight or CG limits for the established fleet weight,  the empty weight for that aircraft should be reestablished.  This may be done by moving the aircraft to another group, or  reestablishing new fleet operating empty weights (FOEWs) Some large transport airplanes have an onboard aircraft  weighing system (OBAWS) that, when the aircraft is on the  ground, gives the flight crew a continuous indication of the  aircraft total weight and the location of the CG in percent MAC. Procedures are required to ensure the onboard weight  and balance system equipment is periodically calibrated in  accordance with the manufacturer’s instructions.  An operator may use an onboard weight and balance  system to measure an aircraft’s and balance as a  primary means to dispatch an aircraft, provided the FAA  has certified the system and approved the system for use in  an operator’s weight and balance control program. As part  of the approval process, the onboard weight and balance  system must maintain its certificated accuracy. The accuracy  demonstration test is provided in the maintenance manual  portion of the Supplemental Type Certificate (STC) or type  certificate of the onboard weight and balance system. The system consists of strain-sensing transducers in each  main wheel and nosewheel axle, a weight and balance  computer, indicators that show the gross weight, the  CG location in percent MAC, and an indicator of the ground  attitude of the aircraft. The strain sensors measure the amount each axle defl cts and  sends this data into the computer, where signals from all of  the transducers and the ground attitude sensor are integrated.  The results are displayed on the indicators for the flight crew.  Using an onboard weight and balance system does not relieve  an operator from the requirement to complete and maintain  a load manifest.  Operational empty weight (OEW) is the basic empty weight  or fl et empty weight plus operational items. The operator has  two choices for maintaining OEW. The loading schedule may  be utilized to compute the operational weight and balance of  an individual aircraft, or the operator may choose to establish  fleet empty weights for a fleet or group of aircraf Reestablishing the OEW Operational Empty Weight (OEW) Fleet Operating Empty Weights (FOEW)  Onboard Aircraft Weighing System The location of the CG in percent MAC must be known in  order to set the stabilizer trim takeoff.  [Figure 9-8] The OEW and CG position of each aircraft should be  reestablished at the reweighing. In addition, it should reestablished through calculation whenever the cumulative  change to the weight and balance log is more than plus or  minus one-half of 1 percent (0.5 percent) of the maximum  landing weight, or whenever the cumulative change in the  CG position exceeds one-half of 1 percent (0.5 percent) of the  MAC. In the case of rotorcraft and aircraft that do not have a  Determine the distance from the CG to the LEMAC by  subtracting the distance between the datum and LEMAC from  the distance between the datum and the CG.  [Figure 9-7] Figure 9-6.  Determining the location of the CG in inches aft of  the datum. Figure 9-7.  Determining the distance from the CG to the LEMAC. Figure 9-8.  Determining the location of the CG in percent MAC. ( ) CG inches aft of datum = × 1,000 Total moment index Total weight ( ) = × 1,000 161,646 177,710 = 909.6 inches Distance CG to LEMAC = Datum to CG – Datum to LEMAC = 49.1 inches = 909.6 – 860.5 ( ) CG % MAC = × 100 Distance CG to LEMAC MAC ( ) = × 100 49.1 180.9 = 27.1%