Definition
The lowest published altitude at which an aircraft using GNSS (satellite-based navigation, such as GPS) for course guidance is guaranteed both adequate satellite-signal reception and obstacle clearance along a given airway or route segment when operating under Instrument Flight Rules.
Plain English
On a route segment flown using GPS, this is the lowest altitude you are allowed to fly that still keeps you safely above terrain and obstacles and high enough for the satellites to work reliably.
Context Anchor
Seen on IFR en route charts where a route segment has a specific minimum altitude for aircraft using approved GNSS navigation.
Derivation
GNSS stands for Global Navigation Satellite System, the general term for satellite navigation networks (GPS is the U.S. version). MEA stands for Minimum En Route Altitude. Putting GNSS in front of MEA simply tells the pilot this minimum altitude applies when the route is being flown by satellite navigation, which has different signal-reception needs than ground-based aids.
Why Pilots Care
It often permits a lower altitude than the conventional MEA, giving pilots better terrain clearance options and more efficient routing on GNSS-equipped aircraft.
Intuition Check
Do not read “minimum” as “recommended.” Here it means the lowest protected altitude allowed for that GNSS-based IFR route segment.
Example Sentence 1
On this segment the GNSS MEA is 4,000 feet, so we can file and fly the airway 1,000 feet lower than the standard MEA shown.
Example Sentence 2
The enroute chart showed a GNSS MEA of 5,000 feet for the segment, lower than the standard MEA.