Which parameter in the FMS is used to balance fuel versus time for cruise optimization?

• A. Altitude selection
• B. Cost index
• C. Wind correction
• D. Thrust setting

Answer: (B)

In cruise optimization, the FMS balances fuel versus time using the cost index. This value expresses how much you value time costs relative to fuel costs. A higher cost index weights time more, so the system favors a faster cruise profile (higher speed, potentially different altitude) even if that means more fuel burn. A lower cost index emphasizes fuel efficiency, leading to slower speeds and more economical cruise settings to save fuel at the expense of longer flight time. Other inputs like altitude selection, wind correction, and thrust setting influence efficiency and path, but they don’t encode the explicit fuel-versus-time trade-off in the same way the cost index does.