Unless otherwise prescribed, what is the rule regarding altitude and course to be maintained during an IFR off-airways flight over mountainous terrain?

When operating under Instrument Flight Rules (IFR) over mountainous terrain, the regulations specify that pilots must maintain a minimum altitude that ensures safety and adequate separation from potential obstacles. The correct guideline is to fly at an altitude of 2,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course being flown. This regulation is designed to provide an extra margin of safety when navigating through areas that may contain high terrain or other obstacles that could pose a risk to flight operations.

Maintaining this altitude requirement allows pilots to account for variations in terrain and potential obstructions, thereby reducing the risk of collisions with these obstacles. It also gives pilots a buffer for unexpected altitude deviations, which may occur due to weather, turbulence, or aircraft performance issues. This minimum altitude requirement reflects a more cautious approach in mountain flying, where the terrain can rise sharply and may not be as predictable as in flatter regions.