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Temporary ballast calculation

Aviation Mechanic General (AMG) practice question 21 of 25 on Weight and Balance. ACS element AM.I.C.K8 · 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 loaded airplane weighs 2,500 lb and its CG is 0.5 inch aft of the aft CG limit. Temporary ballast can be placed in a forward compartment located 30 inches forward of the aft limit. How much ballast is needed?

  1. AAbout 42 lb, rounded up to the next whole pound
  2. BAbout 41 lb, rounded down to the nearest whole pound
  3. CExactly 41.67 lb, with no rounding applied
Show the answer and explanation

Correct answer: A. About 42 lb, rounded up to the next whole pound

  • A — correct Ballast = (2,500 lb x 0.5 in) / 30 in = 41.67 lb, and the handbook says the answer is always rounded up to the next higher whole pound, giving 42 lb.
  • B — incorrect Rounding down would leave the CG slightly outside the limit; ballast is always rounded up.
  • C — incorrect The computed value is 41.67 lb, but the handbook requires rounding up to the next higher whole pound.

BACKGROUND

The CG of a loaded airplane can be moved into its allowable range by shifting passengers or cargo or by adding temporary ballast. The temporary ballast formula is: ballast weight needed = (total weight x distance needed to shift the CG) / (distance between the ballast and the desired CG). The loaded weight used is what the airplane weighed when the CG was out of limits, the distance needed is the difference between the CG location and the exceeded limit, and the ballast arm is measured from the affected limit. The handbook's example gives 46.68 lb, which is rounded up to 47 lb, and the ballast weight is then plugged back into the four-column calculation to confirm the new CG.

STUDY TIP

Set up the formula with the affected limit as the reference, compute, round up, then re-check the CG with the ballast added.

KEY POINTS

  • Ballast = (weight x shift needed) / (ballast distance from desired CG).
  • 2,500 x 0.5 / 30 = 41.67 lb.
  • Always round ballast up to the next whole pound.

SOURCES

  • FAA-H-8083-30B ch06 "Temporary Ballast Formula"
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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.