VASI Lights: How to Read 2-Bar and 3-Bar VASIs, and Why They Are Disappearing

VASI lights are rows of lights beside a runway that tell a pilot on final approach whether they are too high, too low or on the glide path. VASI stands for Visual Approach Slope Indicator. Each light shows white from above its beam angle and red from below it.

On a standard two-bar VASI, red over white means you are on the glide path, normally 3 degrees. White over white means too high, and red over red means too low.

They are also becoming rare. The FAA’s own airport database for October 2026 lists a VASI on just 522 US runway ends, against 6,952 with the newer PAPI.

What Is a VASI?

A VASI is a visual glide slope indicator: a set of lights near the approach end of a runway that gives vertical guidance without any equipment in the cockpit. The runway itself shows a pilot left and right. The VASI answers the harder question of height.

The FAA describes VASI installations of 2, 4, 6, 12 or 16 light units arranged in bars called the near, middle and far bars. Most have two bars, near and far.

Installations of 2, 4 or 6 units sit on one side of the runway, usually the left. The 12- and 16-unit versions put lights on both sides.

According to the Aeronautical Information Manual (AIM), VASI lights are visible from 3 to 5 miles in daylight and up to 20 miles or more at night. That reach is why a VASI helps pilots flying under visual flight rules find a safe descent path long before the runway markings are readable.

How to Read a 2-Bar VASI

A two-bar VASI gives one glide path, normally set at 3 degrees. From the cockpit the far bar, farther down the runway, appears above the near bar, so pilots read it top to bottom.

Flight instructors teach the colors with a rhyme that has several endings. The common version:

White over white, check your height.
Red over white, you’re all right.
Red over red, you’re dead.

On a stable approach the picture stays red over white all the way down. In practice the bars flicker between readings as the pilot corrects, and a drift toward red over red needs an immediate fix.

White over red never appears. The far bar turns white at a higher angle than the near bar, so there is no position where you are above the far bar’s beam but below the near bar’s.

How a 3-Bar VASI Works

A three-bar VASI adds a middle bar and creates two glide paths. The lower one, formed by the near and middle bars, is normally 3 degrees. The upper one, formed by the middle and far bars, is normally a quarter of a degree higher.

The upper path is meant only for high-cockpit aircraft. A pilot sitting high above the main landing gear who flew the lower path would cross the threshold with the wheels too low, so the steeper path restores a safe threshold crossing height.

Reading it is a matter of which pair to watch. A small airplane flies the bottom two bars, wanting the middle bar red and the near bar white. A widebody pilot flies the top two, wanting the far bar red and the middle bar white.

Three-bar VASIs are almost gone in the US. The October 2026 FAA data shows only four runway ends with a six-box VASI, one of them runway 8 at Albuquerque International Sunport.

How VASI Lights Work

The whole system rests on one trick. Each light unit projects a beam that is white in its upper part and red in its lower part, and the unit is aimed so the color boundary sits at a set angle above the ground.

Look at the unit from above that angle and you see white. Drop below it and you see red. Two bars aimed at slightly different angles, one behind the other, create a narrow band where the far bar is red and the near bar is white: the glide path.

Not every VASI is set to 3 degrees. The AIM allows angles as high as 4.5 degrees where obstacles demand it, and warns that angles above 3.5 degrees can lengthen the runway a high-performance aircraft needs to land and stop.

In the FAA’s October 2026 data, 374 of the 522 US VASI runway ends are set at 3 degrees, and 71 are set at 3.5 or 4 degrees. The FAA records the angle for every runway end in that same data.

At selected airports, often ones without a full-time tower, pilots can switch the VASI on themselves by radio. The AIM’s pilot-controlled lighting tables include VASI, which runs at low intensity at night and high intensity by day, set by a photocell.

Why Pilots Need a VASI

Judging height on final approach by eye is harder than it looks, and the FAA lists specific runway shapes that fool pilots. The AIM names VASI systems as one of the defenses against these illusions.

Narrow runways. A runway narrower than the pilot is used to creates the illusion of being higher than you are. A pilot who trusts that picture flies a lower approach and risks hitting objects short of the runway or landing short. A wider runway does the opposite.

Sloping runways. An upsloping runway or upsloping terrain also makes a pilot feel too high, which again leads to a low approach. A downsloping runway has the opposite effect.

Unfamiliar airports make it worse, because the cues a pilot learned at home, such as the runway markings and the size of the runway in the windshield, no longer match. Night approaches over dark terrain remove even more of them.

The Rule: Stay On or Above the VASI Glide Path

A VASI is not just advice in controlled airspace. Under 14 CFR 91.129(e)(3), a pilot of an airplane approaching a runway served by a VASI must stay at or above the glide path until a lower altitude is needed for a safe landing.

That rule sits in the Class D airspace section, and the Class C rules in 91.130 require compliance with 91.129 as well. The regulation allows normal bracketing above and below the glide path to stay on it, so a brief red over red while correcting is not a violation.

A neighboring paragraph, 91.129(e)(2), sets the same at-or-above rule for large or turbine-powered airplanes flying an instrument approach with vertical guidance. Where local obstacles demand it, a VASI beam can also be narrowed, shortened or offset from the centerline, and the Chart Supplement or a NOTAM says so.

VASI vs PAPI: Why VASIs Are Disappearing

The PAPI, or precision approach path indicator, uses the same red and white light units but puts them in a single row of two or four lights, normally on the left side of the runway. Pilots read it left to right instead of top to bottom.

A four-light PAPI gives five readings where a VASI gives three. Two white and two red is on the glide path, three white is slightly high, four white is high, three red is slightly low and four red is low.

The AIM gives PAPI lights a range of about 5 miles by day and up to 20 miles at night, with obstruction clearance out to 3.4 nautical miles. Internationally the shift happened first: ICAO deleted the simple VASIS from Annex 14, its aerodrome standard, in 1995.

The US has followed. We counted every visual glide slope indicator in the FAA’s National Airspace System Resources (NASR) airport file for the cycle effective October 1, 2026. The table shows the result.

Alaska has the most VASI runway ends of any state, 55, followed by California with 54 and Texas with 40. They turn up at every type of airport in the data, from municipal fields to international airports.

For a pilot, the practical upshot is simple: learn both, because the airport you divert to may still have the older system.

Other Visual Glide Slope Indicators

Several other systems share the VASI name or do the same job. All are uncommon, which is exactly why pilots get caught out by them.

Tri-Color VASI

A tri-color VASI is a single light unit that projects three colors: amber above the glide path, green on it and red below it. The AIM gives it a useful range of about half a mile to a mile by day and up to 5 miles at night.

It has a trap. Descending below the glide path, a pilot passes through a small band of dark amber between the green and the red, which must not be mistaken for the amber “too high” signal.

Pulsating VASI (PVASI)

A pulsating VASI is also a single light, using red and white plus a pulse. The AIM lists these indications:

• Pulsating white: above the glide path
• Steady white, or alternating red and white: on the glide path
• Steady red: slightly below the glide path
• Pulsating red: further below the glide path

The pulse gets faster the farther the aircraft strays above or below the glide path. Its useful range is about 4 miles by day and up to 10 miles at night.

Alignment of Elements

The cheapest system has no lights at all. Painted plywood panels, normally black and white or fluorescent orange, stand at different heights near the runway, and the pilot flies so they line up. Some are lit for night use, and their useful range is about three-quarters of a mile.

T-VASIS and AT-VASIS

ICAO standards also describe a T-shaped system. T-VASIS has 20 light units in two wing bars with a line of “fly-up” and “fly-down” lights through each, and AT-VASIS is a 10-unit, one-sided version.

Those are fading too. An ICAO Annex 14 recommendation says their use as standard systems should be discontinued as of January 1, 2020, leaving PAPI and its two-light version, APAPI, as the systems of choice.