When outside controlled airspace, what is the minimum altitude above the highest terrain that an aircraft must maintain?

The correct choice is based on regulations regarding altitude restrictions for aircraft flying outside controlled airspace. According to FAA regulations, when operating outside controlled airspace, an aircraft is required to maintain a minimum altitude of at least 1,000 feet above the highest terrain or obstacle within a horizontal distance of 2,000 feet of the aircraft.

If the area being flown over is mountainous, the regulation specifies that the minimum altitude increases to 2,000 feet above the highest terrain within a horizontal distance of 4 nautical miles. Therefore, the choice of 1,500 feet is incorrect because it does not meet the regulatory minimums outlined for flight in those conditions.

The correct understanding of this requirement ensures safety by providing adequate vertical separation from terrain, particularly in areas with higher elevations or obstacles. Choosing an altitude that exceeds this regulatory minimum is essential for operational safety, serving as a buffer against terrain and other hazards.