Definition
A historical Flight Service component of En Route Flight Advisory Service (EFAS, also known as Flight Watch) that provided weather advisories tailored to aircraft operating at high altitudes, generally at or above FL180. Pilots contacted HI-EFAS in flight to obtain current weather information, hazardous weather updates, and pilot reports relevant to high-altitude operations. The dedicated EFAS/Flight Watch service was discontinued by the FAA in 2015; weather services are now obtained through Flight Service on standard frequencies.
Plain English
HI-EFAS was the name for the in-flight weather service pilots used to call when flying at high altitudes to get current weather updates from a Flight Service specialist. It is no longer a separate service — pilots now call regular Flight Service for the same information.
Context Anchor
Seen in FAA acronym lists, weather-service references, and older in-flight weather advisory material.
Derivation
‘HI’ marks the high-altitude version of EFAS. ‘En Route’ means while flying along the route, ‘Flight Advisory’ means weather advice given to pilots, and ‘Service’ means a facility staffed to provide it. Knowing the parts makes it easier to recognise the older ‘Flight Watch’ name when it appears in study materials.
Why Pilots Care
Provides timely weather and operational support that improves situational awareness and safety on high-altitude flights.
Intuition Check
HI-EFAS is not a cockpit instrument or an aircraft system. It refers to weather advisory help for aircraft already flying high along their route.
Example Sentence 1
The training manual still mentioned HI-EFAS, but the instructor explained that high-altitude weather updates are now obtained directly from Flight Service.
Example Sentence 2
HI-EFAS relayed updated winds aloft that helped the crew adjust their altitude for better fuel efficiency.