where the datum is located. In addition to overloading or drastically reducing the  aircraft’s weight, the distribution of weight is also a concern.  When aircraft equipment is changed, the person making the  equipment change must make an entry on the equipment list  indicating items added, removed, or relocated; the date of  the change; and the person’s name and certification number  in the aircraft’s maintenance records. For the purpose of weight and balance computations, the CG  of an airplane is an imaginary point about which the nose- heavy (–) moments and tail-heavy (+) moments are exactly  equal in magnitude. If suspended from the CG point, the  aircraft would have no tendency to rotate nose up or nose  down. The CG of the loaded aircraft can range fore and aft  within certain limits that are determined during the fl ght test  for type certific tion. These limits are the most forward- and  rearward-loaded CG positions at which the aircraft meets the  performance and flight characteristics required by the FAA.  Any loading that places the CG outside the limits for a  particular aircraft seriously impairs the pilot’s ability control the aircraft. For example, it is more difficult to take  off and gain altitude in a nose-heavy aircraft, and the aircraft  tends to drop its nose when the pilot reduces throttle. It also  requires a higher speed to land safely. A tail-heavy aircraft is  more susceptible to stalling at low speed, which is a concern  during the landing approach. On small airplanes and on all helicopters, the CG location  is identified as being a specific number of inches from the  datum. The CG range is identified in the same way. On larger  airplanes, from private business jets to large jumbo jets, the  CG and its range are typically identified in relation to the  width of the wing. The width of the wing, or straight-line distance from the  leading edge to the trailing edge, on an airplane is known as  the chord. If the leading edge and the trailing edge of a wing  are parallel, the chord is equal at all points along the entire  length of the wing. The average length of the chord, or MAC,  of a tapered wing is more complicated to define. The MAC,  as seen in  Figure 3-16 , is the chord of an imaginary airfoil  that has the same aerodynamic characteristics as the actual  airfoil. You can also think of it as the chord drawn through  the geographic center of the plan area of the wing. Theweightandbalancedataoftheairplanein  Figure3-17  states  that the MAC is from stations 144 to 206 and the CG is  located at station 161. The relative positions of the CG and the aerodynamic  center of lift of the wing have critical effects on the flight characteristics of the aircraft. Consequently, relating the  CG location to the chord of the wing is convenient from  a design and operations standpoint. Normally, an aircraft  has acceptable fl ght characteristics if the CG is located  somewhere near the 25 percent average chord point. This  means the CG is located one-fourth of the distance back from  the LEMAC to the TEMAC. Such a location places the CG  forward of the aerodynamic center for most airfoils. weight and balance computations, the MAC is established  by the manufacturer, defining its leading edge (LEMAC)  and trailing edge (TEMAC) in terms of inches from the  datum.  [Figure 3-16]  The CG location and various limits  are then expressed in percentage of the chord or percent  MAC. In order to relate the percent MAC to the datum, all  weight and balance information includes two items: the MAC  length in inches and the location of the LEMAC in inches  from the datum. For the purpose of simplicity, most light- aircraft manufacturers express the CG range in inches from  the datum; transport-category aircraft CGs are expressed in  percent MAC. Center of Gravity (CG) and Mean  Aerodynamic Chord (MAC) Center of Gravity (CG) Figure 3-16.  The MAC is the chord drawn through the geographic  center of the plan area of the wing. Mean Aerodynamic Chord (MAC) Usually listed in the aircraft’s TCDS when it is required for  3-8 CG MAC Trailing edge mean  aerodynamic chord Leading edge mean  aerodynamic chord TEMAC LEMAC Datum MAC = TEMAC – LEMAC MAC = 206" – 144"  MAC = 62"