At what flight level is an aircraft cleared to descend if it is operating at FL310?

The correct answer indicates that an aircraft operating at FL310 is cleared to descend to 12,000 feet. This is reasonable based on standard separation procedures and the requirements for safe altitude changes in airspace.

When determining the descent clearance, it's essential to consider the altitude levels and the required vertical separation from other aircraft. Generally, if an aircraft is at FL310, it can typically be cleared to an altitude that allows safe vertical separation from other traffic, which is around 1,000 feet or more.

12,000 feet reflects a standard transition point when descending from higher flight levels, often considered for aircraft exiting controlled airspace or before entering terminal airspace. Other options do not typically align with the adequate level of descent from FL310 considering safety protocols and air traffic control standards.