SkyDrill

CG as percent of MAC

Aviation Mechanic General (AMG) practice question 13 of 25 on Weight and Balance. ACS element AM.I.C.K4 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA large airplane has its CG located 660 inches aft of the datum. The leading edge of the mean aerodynamic chord (LEMAC) is 600 inches aft of the datum, and the MAC is 200 inches long. Expressed as a percent of MAC, the CG is at

  1. A10 percent MAC, using LEMAC as the divisor
  2. B30 percent MAC
  3. C60 percent MAC
Show the answer and explanation

Correct answer: B. 30 percent MAC

  • A — incorrect The difference between CG and LEMAC is divided by the length of the MAC, not by the LEMAC distance.
  • B — correct Percent of MAC = (CG - LEMAC) / MAC x 100 = (660 - 600) / 200 x 100 = 30 percent.
  • C — incorrect 60 is the distance in inches between the CG and LEMAC; it still has to be divided by the 200-inch MAC and multiplied by 100.

BACKGROUND

On small airplanes and helicopters the CG is given in inches from the datum, but on larger airplanes the CG and its range are usually expressed in relation to the width of the wing, the mean aerodynamic chord (MAC). To convert a CG in inches to percent of MAC, identify the CG location and the leading edge of the MAC (LEMAC), both in inches from the datum, subtract LEMAC from the CG, divide by the length of the MAC, and multiply by 100. The handbook's example uses a CG of 945 inches, a LEMAC of 900 inches, and a MAC of 180 inches to arrive at 25 percent MAC.

STUDY TIP

Write the formula first, Percent MAC = (CG - LEMAC) / MAC x 100, then substitute; most errors come from dividing by the wrong number.

KEY POINTS

  • Large airplanes state CG as percent of MAC.
  • Subtract LEMAC from CG, divide by MAC, multiply by 100.
  • (660 - 600) / 200 x 100 = 30 percent.

SOURCES

  • FAA-H-8083-30B ch06 "Mean Aerodynamic Chord"
Practice the Aviation Mechanic General (AMG) test →Timed 60-question exam, by ACS area, or review your misses. Free.
MORE ON WEIGHT AND BALANCE

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.