Trapped fuel may result in a cg that is as much as ___% MAC farther aft.

• A. 0%
• B. 1%
• C. 2%
• D. 3%

Answer: (D)

Understanding how fuel distribution affects the center of gravity is key. Even when you think all fuel is accounted for, some fuel can remain trapped in tanks or plumbing and not drain or shift as expected. That trapped fuel effectively moves the aircraft’s weight aft, pushing the center of gravity toward the aft limit.

In the P-8A (and many transport airframes), the worst‑case aft shift due to trapped fuel is limited to three percent of the mean aerodynamic chord. That means, for weight and balance calculations, you must consider an aft CG offset up to 3% of MAC to ensure the aircraft remains within its certified aft limit under that condition.

So the reason 3% MAC is the correct choice is that it represents the maximum aft shift caused by trapped fuel that designers and operators must plan for. The smaller values would underestimate the possible aft shift, and zero would ignore this real effect.

As a quick context, if the MAC were, say, 10 feet, a 3% shift corresponds to about 0.3 feet (roughly 3.6 inches) aft of the nominal CG, which can be enough to impact stability margins and handling if not accounted for.