Questions: Grid navigation is used when operating in the polar region. when operating near the equator. whenever the magnetic variation exceeds 10 degrees. at all times during international flights.

The answer is the first one: when operating in the polar region.

Explanation for each option:

1. When operating in the polar region: Correct. Grid navigation is used in the polar regions because the magnetic compass becomes unreliable due to the proximity to the magnetic poles. Instead, a grid system based on true north is used for navigation.

2. When operating near the equator: Incorrect. Near the equator, magnetic compasses work reliably, and there is no need for grid navigation.

3. Whenever the magnetic variation exceeds 10 degrees: Incorrect. While significant magnetic variation can complicate navigation, grid navigation is specifically designed for polar regions where magnetic compasses are unreliable, not just for areas with high magnetic variation.

4. At all times during international flights: Incorrect. Grid navigation is not required for all international flights, only for those that operate in polar regions where magnetic compasses are unreliable.

Summary: Grid navigation is specifically used when operating in the polar region due to the unreliability of magnetic compasses near the magnetic poles.