Definition
An abbreviation used in NOTAMs and other aeronautical publications to indicate the date and/or time at which a stated change, restriction, or condition becomes active.
Plain English
WEF marks the start point of something. Whatever is being announced takes effect from the date or time shown after WEF.
Context Anchor
Seen in NOTAM contractions and other aviation notices that give start times for closures, changes, or restrictions.
Derivation
Standard administrative shorthand long used in official notices. 'With effect from' simply means 'starting on this date/time,' and the abbreviation keeps NOTAM text short.
Why Pilots Care
Pilots must know the start time to plan flights that comply with updated rules or avoid restricted areas.
Intuition Check
Do not read WEF as a general statement that something has an effect. In aviation notices, it marks the start point: from this time onward, the item applies.
Example Sentence 1
The NOTAM read: 'RWY 09/27 CLSD WEF 15 MAR 0600Z,' meaning the runway would be closed starting at that date and time.
Example Sentence 2
Check the WEF time before assuming the new procedure applies to your departure.