In areas of rapidly rising terrain, what additional feet are added to MEFs?

The correct answer is 250 feet, which is a vital consideration for ensuring safety in areas with rapidly rising terrain. When determining the Minimum Enroute Flight Level (MEFL), pilots must take into account the terrain elevation. In regions where substantial changes in elevation occur quickly, an additional buffer is added to the MEFs to create a safety margin that helps prevent obstacles or terrain from being inadvertently breached by aircraft.

By adding 250 feet to the MEF, air traffic control ensures that aircraft maintain adequate vertical separation from the terrain. This practice minimizes the risk of controlled flight into terrain (CFIT) incidents, particularly under conditions where terrain elevation may not be immediately apparent from the flight path. The 250-foot addition is specifically derived from guidelines that factor in the potential for terrain features to significantly alter elevations in a short distance, providing essential safety assurance for pilots navigating through such landscapes.

In contrast, the other potential heights like 100, 150, and 200 feet do not provide the same level of safety margin needed for rapid rises in terrain. Therefore, while they may be closer to certain technical standards, they are insufficient for the complexity and unpredictability of areas with notable elevation changes.