Definition
In wake turbulence avoidance, the area extending two miles behind a preceding aircraft and within 250 feet of its altitude or below, where wake turbulence from that aircraft is most likely to be encountered.
Plain English
A specific zone right behind another aircraft — about two miles long and within 250 feet of its altitude or lower — where you are most likely to fly into the swirling air it leaves behind.
Context Anchor
Used in ATC spacing and wake-turbulence discussions, especially when one aircraft is departing or landing after another.
Derivation
Directly comes from a Latin root meaning straight. Behind comes from Old English and means at the back of something. The phrase helps you picture one aircraft following the path of another, but in aviation it does not require a perfect tail-to-nose line.
Why Pilots Care
An aircraft directly behind a heavier aircraft risks encountering wake turbulence that can cause loss of control.
Grounding Statement
Picture the first aircraft drawing an invisible line through the air, and the second aircraft flying on or very near that same line.
Intuition Check
Do not assume directly behind means perfectly centered behind the other aircraft. In this FAA use, an aircraft can still count as directly behind if it is close to the earlier aircraft's path.
Example Sentence 1
The pilot delayed takeoff to avoid being directly behind the heavy jet that had just departed.
Example Sentence 2
Avoid flying directly behind a departing jet until it has climbed well above your altitude.