At what altitude is the MEA on a jet route when no MEA is depicted?

When no Minimum Enroute Altitude (MEA) is depicted on a jet route, the standard altitude is considered to be 18,000 feet Mean Sea Level (MSL). This altitude is significant because it is the base of the Flight Level 180 threshold, where jet routes typically begin. At and above this altitude, aircraft can operate in high altitude airspace, which is managed under a different set of regulations and procedures compared to lower altitude airspace.

In the context of air traffic control, the MEA serves multiple purposes, including ensuring terrain clearance and providing radio reception within the route. When a jet route is established and does not specify an MEA, 18,000 feet MSL is the default altitude that gives pilots a clear understanding of operating bounds in the absence of specific altitudes. This altitude helps maintain safety and separation for aircraft operating in the National Airspace System.

Understanding this standard helps pilots and air traffic controllers work efficiently within the airspace system, especially in high altitude environments.