Airplane pilots receive a base salary as compensation.

AUnit Salary Planpays based onunits worked(e.g., miles, credits, or kilometers).

In this case, pilots earn extra based onkilometers flown, makingunit salary planthe correct choice.

It also supportsestimation of wagesfor offer letters since you can project based on expected units.

Why not the others?

A. Unit-based allowance plan→ Allowances are flat recurring payments, not tied to actual units worked.

B. One-time payment→ Used for bonuses or ad hoc payments, not recurring per-unit pay.

D. Period salary plan→ Handles additional pay periods, not per-unit payments.