Definition
A series of sequenced flashing lights installed on the extended centerline of a runway, leading inbound to the runway threshold. RAIL is a component of certain approach lighting systems (such as ALSF-1, ALSF-2, MALSR, and SSALR) and helps the pilot visually identify the runway centerline alignment during the final stages of an instrument approach.
Plain English
A line of fast-flashing lights pointing toward the start of the runway, helping the pilot line up correctly when breaking out of the clouds on an approach.
Context Anchor
Seen in instrument approach lighting descriptions and in discussions of what to do when approach lighting components are inoperative.
Derivation
The phrase is descriptive: 'alignment' comes from the French 'aligner,' meaning to arrange in a straight line. The lights are literally arranged in a line to show alignment with the runway.
Why Pilots Care
They provide immediate visual confirmation of runway alignment, allowing safe continuation of the approach when other references are limited.
Intuition Check
Do not think of RAIL as ordinary runway lights along the pavement. They are approach lights that help show the runway’s alignment before or as the pilot reaches the runway area.
Example Sentence 1
As we descended through the cloud layer, the sequenced flashing of the RAIL drew our eyes straight to the runway threshold.
Example Sentence 2
With the RAIL visible, the crew continued the approach even though the runway itself was not yet in sight.