Definition
A pair of synchronized flashing white lights installed on either side of the runway threshold to provide rapid and positive identification of the approach end of a runway. REILs may be either omnidirectional or unidirectional facing the approach area, and are commonly installed at runways that lack other approach lighting systems or where the threshold is otherwise difficult to identify against surrounding lights or terrain.
Plain English
Two bright white strobes that flash together, one on each side of the start of the runway, to help a pilot pick out where the runway begins.
Context Anchor
Seen in airport lighting descriptions, instrument approach information, and notices about inoperative runway equipment.
Why Pilots Care
Provides immediate visual confirmation of the runway threshold when approach lighting systems are out or unavailable.
Intuition Check
Do not confuse REIL with the normal lights along the runway edges. REIL are flashing identification lights at the approach end of the runway, not continuous lights running down the runway.
Example Sentence 1
The field was hard to find against the city lights, but the REILs flashing at the threshold made the runway easy to identify.
Example Sentence 2
With the REIL reported inoperative, the crew increased their scan for other runway markings during the night arrival.