What is the minimum en route altitude along a jet route?

The minimum en route altitude along a jet route is 18,000 feet Mean Sea Level (MSL). Jet routes are specifically designed for aircraft operating in the high-altitude en route environment, primarily used by aircraft flying at altitudes above 24,000 feet. However, the transition into the jet route structure begins when an aircraft reaches 18,000 feet, aligning with the Federal Aviation Administration (FAA) regulations that define the airspace structure for flight operations. This altitude marks the boundary where high altitude air traffic control applies, meaning that once an aircraft is at or above this altitude, it is required to navigate according to the jet route system and file an IFR (Instrument Flight Rules) flight plan if it plans to operate in the controlled airspace. Knowing this is essential for understanding how to properly operate within the jet route framework during instrument flight operations.