REIL and RAIL: the Two Sets of Flashing White Lights That Are Not the Same Thing, and Why the Distinction Matters on Every Night Approach

REIL (Runway End Identifier Lights) and RAIL (Runway Alignment Indicator Lights) are two separate runway lighting systems that both flash white at night and are routinely confused - even by experienced pilots. Understanding the difference is not academic: at 200 feet on an ILS approach in a 200-foot ceiling, knowing which set of lights you’re looking at determines whether you continue or go around.

Why Airport Lighting Systems Were Designed This Way

Post-World War II aviation drove rapid development of structured approach lighting. As aircraft got faster and instrument approaches became routine, pilots needed organized visual information to bridge the gap between instrument flight and visual landing. Breaking out of clouds at a few hundred feet - in reduced visibility, in an unfamiliar environment, with seconds to identify the runway, confirm alignment, and assess glidepath - demanded a purpose-built visual system.

REIL and RAIL both emerged from that era to solve two distinct problems.

What Are Runway End Identifier Lights (REIL)?

REIL answers one question: where is the threshold?

A REIL installation consists of two synchronized white strobe lights, one on each side of the runway threshold, mounted at the threshold itself and aimed outward toward the approach. Both lights fire simultaneously - not alternating, not in sequence. Together, dark, together again.

They’re visible from 3 to 5 miles in good conditions, sometimes farther. In a visual environment crowded with roads, shopping centers, and antenna farms, those two synchronized high-intensity strobes identify the precise start of the landing surface. That is the entirety of their job.

Not every runway has them. Whether a runway gets REIL depends on the visual environment, traffic volume, available budget, and airport planning decisions. The Chart Supplement entry for any airport lists installed runway lighting.

What Are Runway Alignment Indicator Lights (RAIL)?

RAIL answers a different question: am I aligned with the centerline?

Runway Alignment Indicator Lights are not at the threshold. They extend outbound from the threshold into the approach path, providing a series of sequenced flashers that appear to travel toward the runway. Pilots call this the rabbit - a fast pulse of white light that appears to rush inbound, like a wave rolling toward shore.

The flash sequence fires so quickly that the eye perceives motion rather than individual pulses. One complete cycle takes approximately one second, and the apparent direction of motion is always inbound, toward the runway. At night, in reduced visibility, the rabbit commands attention and draws a visual line from your current position toward the threshold.

RAIL is a component of larger, standardized approach lighting systems - not a standalone installation.

Which Approach Lighting Systems Include RAIL?

RAIL appears in several FAA-codified configurations, identifiable by their designations on instrument approach procedure charts:

ALSF-1 and ALSF-2 (Approach Lighting System with Sequenced Flashers): high-intensity systems at major airports on precision approach runways, extending up to 2,400 feet from the threshold.
MALSR (Medium Intensity Approach Lighting System with Runway Alignment Indicator Lights): extends 1,400 feet from the threshold.
SSALR (Simplified Short Approach Lighting System with RAIL): a scaled-down version for runways where a full ALSF installation isn’t practical.

The R at the end of MALSR and SSALR is the indicator - that R means runway alignment indicator lights are part of the system. When you see that letter in an approach lighting designation, the rabbit is included.

Approach lighting system diagrams appear in the profile view on instrument approach procedure charts. Learning to read those symbols quickly is part of a thorough approach briefing before leaving the ground.

Does Seeing REIL Count as Visual Contact Under FAR 91.175?

No. This distinction is operationally critical.

FAR 91.175 governs operations at and below instrument approach minimums. To descend below decision altitude or minimum descent altitude, specific visual references must be in sight. The approach lighting system - which includes RAIL - is on the FAA’s acceptable references list. A REIL is not.

Two synchronized threshold strobes do not satisfy the visual reference requirement for continuing below minimums. Seeing the approach lighting system with RAIL does - with one additional constraint: descent cannot continue below 100 feet above touchdown zone elevation using approach lights alone unless the red terminating bars or red side row bars marking the inner portion of the system are also visible.

Consider a night Category I ILS approach with a 200-foot ceiling: you break out and see white flashing lights ahead. Is this the threshold REIL, or is this the RAIL-equipped approach lighting system still extending outbound from the threshold? If it’s the REIL, you are close to the threshold. If it’s the approach lighting system with RAIL, significant distance remains on the glideslope. That distinction drives the continue-or-go-around decision, and it needs to be sorted out before the approach, not during it.

How REIL, RAIL, VASI, and PAPI Work Together

Each system answers a different question. Confusing their roles creates gaps in situational awareness.

REIL - Where is the threshold?
RAIL - Am I aligned with the centerline?
VASI/PAPI - Is my glidepath correct? (Red over white means you’re all right; red over red means dangerously low; white over white means too high.)

Together, these systems provide a complete picture of the approach environment. Independently, each one answers only its own question.

RAIL also provides depth cue information that matters for VFR night pilots, not just IFR pilots. Runway foreshortening - a documented visual phenomenon where a runway at night can appear closer or at a different angle than it actually is - is partially countered by the approach lighting system. The rabbit, appearing to rush toward the aircraft, reinforces the sense of remaining distance. Decades of FAA safety research have consistently documented the correlation between approach lighting availability and accident reduction.

How to Activate REIL with Pilot-Controlled Lighting

At non-towered airports, pilot-controlled lighting activates via the Common Traffic Advisory Frequency (CTAF). Key the microphone the appropriate number of times within a five-second window:

7 clicks - high intensity
5 clicks - medium intensity
3 clicks - low intensity

Where REILs are part of the pilot-controlled lighting system, they come on with the runway edge lights. Activate pilot-controlled lighting 10 or more miles out - before you’re close enough to need it urgently - to build the visual picture before the approach gets busy.

At towered airports, the controller manages lighting intensity, and REIL can sometimes be adjusted or disabled independently. If threshold identification is difficult in a complex visual environment, asking the controller to confirm REIL is on at maximum intensity is a reasonable and routine request.

What to Check in NOTAMs Before Any Night Flight

Approach lighting systems are electrical infrastructure. They fail, sustain storm damage, and go out of service for maintenance. The NOTAM system is how that information reaches pilots before flight.

Before any night flight, the NOTAM check should specifically include lighting outages at the destination and all alternates.

When the approach lighting system is out of service, instrument approach minimums increase. The FAA publishes separate minimums for approaches without approach lighting, printed on the approach plate in a separate column or with a specific notation. A NOTAM showing approach lighting out of service means the effective minimums for that approach have changed - plan for the higher number.

For VFR night pilots, a NOTAM showing REIL out of service means threshold identification just got harder. That’s not a reason to cancel, but it is a reason to adjust: fly a wider pattern, allow more time on final to acquire the runway environment. Treat lighting NOTAMs as an operational change to the environment, with the same weight as an updated weather observation.

Key Takeaways

REIL = two synchronized white strobes at the threshold, facing outbound. Purpose: identify the start of the landing surface. Visible 3–5 miles out.
RAIL = sequenced flashers (the rabbit) extending outbound from the threshold, up to 2,400 feet. Purpose: provide centerline alignment and depth cues throughout the approach.
REIL does not satisfy the visual reference requirement under FAR 91.175 for continuing below instrument minimums. The approach lighting system (which includes RAIL) does.
Approach lighting system designations ending in R - MALSR, SSALR - include RAIL. ALSF-1 and ALSF-2 include RAIL at high intensity.
Always check lighting NOTAMs before a night flight - approach lighting outages directly change your effective IFR minimums and require replanning.