Definition
A specialized in-flight weather service, formerly known as Flight Watch, that provided pilots en route with timely, real-time weather information tailored to the type of flight, route, and altitude. EFAS was operated by Flight Service Stations on the dedicated frequency 122.0 MHz below 18,000 feet MSL. The service was officially discontinued by the FAA in 2015, with its functions absorbed into standard Flight Service on regular FSS frequencies.
Plain English
A radio service pilots once used to get up-to-the-minute weather information while flying. It had its own frequency (122.0) and call sign (Flight Watch). It was retired in 2015, but the acronym still appears in older handbooks and study material.
Context Anchor
Seen in older FAA handbooks, acronym lists, and weather-related instrument flying discussions.
Derivation
"En-route" comes from the French en route, meaning "on the way." "Advisory" comes from Latin advisare, "to consider or counsel." Together: counsel given to a pilot while on the way — which is exactly what the service provided.
Why Pilots Care
Gives pilots real-time weather information so they can avoid hazards and make safer route decisions.
Intuition Check
Do not read “advisory” as a command or clearance. EFAS provided helpful weather information; the pilot still made the flight decision.
Example Sentence 1
The handbook still references EFAS, but pilots today contact Flight Service directly for en-route weather updates.
Example Sentence 2
EFAS advised the pilot of icing conditions reported ahead and suggested an altitude change.