At what altitude is a minimum vertical separation of 2000 feet required for IFR flights?

The required minimum vertical separation of 2000 feet for IFR flights begins at Flight Level 290 (FL290) and continues up to Flight Level 410 (FL410). When aircraft are flying at altitudes above this level, specifically at FL410 and above, they must adhere to the 2000-foot vertical separation standard. This regulation is crucial for maintaining safe distances between aircraft to prevent potential mid-air collisions and ensure safe navigation in controlled airspace, particularly at higher altitudes where air traffic density may increase.

The answer given refers to FL410, accurately indicating that at this altitude and above, the 2000-foot vertical separation is mandated. Other choices such as FL360, FL450, and FL500 do not align with the altitude threshold where this requirement starts. Specifically, FL450 and FL500 are above the minimum requirement but do not mark the initiation of the standard. Thus, FL410 is the correct designation of the altitude for this regulation.