When is an alternative required for a Navy IFR flight plan?

An alternative is required for a Navy IFR flight plan when the destination is forecasting a ceiling below 3000 feet or visibility is less than 3 statute miles. This requirement is in place to ensure safety during flights, especially in situations where weather conditions are marginal or could deteriorate, which might restrict a pilot's ability to land safely at the intended destination.

When the forecast indicates a ceiling below 3000 feet, it suggests limited vertical visibility, which can complicate approaches and landings. Similarly, if visibility dips below 3 statute miles, the potential for navigation difficulties and the inability to see the runway while on approach increases as well. Thus, having an alternative airport in mind provides a backup option for pilots, ensuring they can divert to a safer location should conditions at the primary field not be suitable for landing.

The other options do not encapsulate the same clarity in defining when an alternative is required, focusing instead on distance or flight duration, which do not directly correlate with immediate weather-related safety needs at an airport.