Definition
The lowest published altitude on a route segment that may be flown under IFR when navigating by GNSS (satellite-based navigation). It guarantees adequate obstacle clearance and, where required, acceptable GNSS signal performance for the segment.
Plain English
It is the lowest altitude you are allowed to fly on a particular leg when you are flying that leg using GPS for navigation. Below it, you cannot guarantee terrain clearance or reliable GPS-based navigation on that segment.
Context Anchor
Seen on IFR en route charts and route planning information for routes or segments that rely on satellite navigation.
Derivation
‘Minimum En Route Altitude’ is the long-standing IFR concept of the lowest legal cruising altitude on a route. The ‘GNSS’ prefix simply marks that this version of the MEA applies when the segment is flown using satellite navigation, which can sometimes allow a lower minimum than the ground-based-navaid version.
Why Pilots Care
It can allow a lower altitude than the standard MEA on some routes, saving fuel and providing better terrain clearance options when flying with GPS or other satellite systems.
Intuition Check
Do not read GNSS MEA as a recommended or comfortable cruise altitude. It is a published minimum altitude for that route segment based on obstacle clearance and satellite navigation reception.
Example Sentence 1
On this leg the GNSS MEA is 6,000 feet, so we will cruise at 7,000 once cleared.
Example Sentence 2
The chart showed a GNSS MEA lower than the regular MEA, allowing a more efficient IFR routing.