Definition
The time the pilot expects the aircraft to arrive over a specified fix or destination, based on current groundspeed, route, and remaining distance. ETA is normally expressed in Coordinated Universal Time (UTC, also called Zulu time) and is updated in flight as conditions change.
Plain English
Your best guess of what time you will get there, worked out from how fast you are going and how far you still have to fly.
Context Anchor
Pilots use ETA in flight planning, navigation logs, position reports, and radio calls with air traffic control.
Derivation
From the Latin aestimare, meaning 'to value or judge.' An ETA is a judged time — a calculated prediction, not a fixed promise. Knowing this reinforces that the figure is expected to be revised as the flight progresses.
Why Pilots Care
ATC uses your ETA for separation and sequencing, search and rescue uses it to know when to start looking for you if you don't arrive, and you use it to manage fuel reserves and alternate decisions. An inaccurate or unrevised ETA can cause real operational and safety problems.
Intuition Check
ETA is not a guaranteed arrival time. It is an estimate that may change if wind, routing, speed, or delays change.
Example Sentence 1
Center, Skyhawk Three Four Alpha, estimating KILMR at one seven three zero Zulu.
Example Sentence 2
Headwinds caused the crew to revise their ETA by fifteen minutes.