In what scenario is a pilot likely to experience a waiver of standard minimums?

Answer: C — When there is a compelling need to land.

A waiver of standard minimums is often granted in situations where it's critical for the aircraft to land, particularly when there are compelling reasons that necessitate it. This could include emergencies, such as medical situations on board, mechanical failures, or other urgent circumstances that require the aircraft to land despite weather conditions that would typically not allow such an approach. While training missions might involve specific minimums, they usually adhere to the standard regulations unless special conditions are invoked. Ensuring aircraft safety is paramount, but merely having safety in mind does not justify a waiver. Significant weather changes can also impact operations, but a waiver is more often specific to urgent needs to land rather than changing conditions, which doesn't automatically prompt a deviation from standard minimums. Therefore, the scenario involving a compelling need to land best illustrates the rationale for granting a waiver of standard minimums.