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Should You Follow The PAPI/VASI On Final, Or Aim For The Numbers?


Should you use the PAPI/VASI as a descent aid for final approach, or should you land close to the numbers to avoid wasting valuable runway?

We'll dig into how much room you have to land if you use them all the way to touchdown. But first, let's quickly review PAPIs and VASIs.


Before diving into how you should plan a descent using visual guidance systems, it's important to know a little bit about how they work.

The Precision Approach Path Indicator (PAPI) uses lights installed in a single row of either two or four light units. In a 4-light setup, two white lights and two red lights mean you're on the established glide path.

These lights are visible from about 5 miles during the day and up to 20 miles at night. The visual glide path of the PAPI typically provides safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 3.4 NM from the runway threshold.

Visual Approach Slope Indicator (VASI) is a system of lights arranged in two separate light banks. If you see two red lights over two white lights, you're on glide path. Although normal glide path angles are 3 degrees, VASI lights at some airports may be as high as 4.5 degrees to give proper obstacle clearance.

These lights are visible from 3-5 miles during the day and up to 20 miles or more at night. The visual glide path of the VASI provides safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 4 NM from the runway threshold.


Choosing Your Aiming Point

In almost every case, following the PAPI or VASI will give a single-engine piston aircraft more than enough room to land and stop well before the end of the runway. It's much more likely for a single-engine piston to land short when aiming for the threshold, than to overrun the runway after touching down near the aiming points.

The runway aiming points (commonly called the 1000 foot markers) are a perfect target to descend towards, and you should plan to touchdown within 200 feet of them. If landing performance allows, having some runway prior to your point of landing will ensure that you don't land short.

Configuration changes, tailwinds, stop-and-go landings, and tailwinds are a few reasons why you might plan to land before the aim point markers, to ensure you have enough usable runway left. Because of that, it's not a firm rule to follow every time you land. But in the majority of cases, using vertical guidance to land in the touchdown zone of the runway is a safer option.


How You Should Fly Referencing The PAPI or VASI

Whether flying during the day or night, vertical guidance lighting is one great reference for you to use on descent. On the base leg of your pattern, if the lights show that you're on glide path, you'll probably end up slightly low. The greater rate of descent typical of turns means you'll lose more altitude quicker than a straight-in descent. Because of that, it's OK to fly slightly higher on base than what the VASI indications suggest.

On final approach, use PAPI/VASI indications to ensure you're flying a stable approach to the runway and aren't chasing the glide path. While it's entirely possible to fly a stabilized approach slightly high or low, the 3-degree glide path has been established as a consistent way to approach the runway without landing short or long.


Landing From An Instrument Approach

One of the most common mistakes pilots make when transitioning from IMC to visual conditions on an instrument approach is to chop the power and dive for the runway. This maneuver inherently de-stabilizes the approach. Unless conditions require the extra few hundred feet of available landing distance you might gain, there's little reason to abandon a glide path in a single-engine piston airplane.


Entering The Flare From The Pattern Or An Approach

As you approach the flare, you'll stop referencing the visual guidance system and start using the runway itself.

Transition your eyes up to the end of the runway and runway edges to judge your height. The closer you get to the runway, the more sensitive the VASI or PAPI becomes and it can be difficult, if not impossible, to follow lights at this point.

Simply put, don't chase the PAPI/VASI at low altitude over the runway.


Exceptions Are Few And Far Between

At nearly every airport equipped with vertical guidance to the runway, you'll fly a standard glide path of 3 degrees. But this isn't the case everywhere.

Pilots are prohibited from referencing the 4-light PAPI at Molokai's Airport (PHMK) beyond 1.8 NM from the landing threshold due to rapidly rising terrain. At Molokai, the PAPI is situated at a steep 4-degree glide path and is installed as a reference for straight-in approach traffic. If you fly the standard traffic pattern at Molokai, there's more than enough room to maneuver and land without terrain conflicts by flying a standard 3-degree glide path. In cases like this, there's nothing wrong with ignoring the visual glide path indications.

Swayne Martin

At Steamboat Springs, Colorado, the 2-light PAPI for Runway 32 is situated at 4 degrees due to rising terrain. The RNAV(GPS)-E approach to this runway requires an extremely steep 7.75 degree descent path from MDA to landing if an aircraft breaks out at minimums. Because of this, instrument traffic usually flies well above the vertical guidance indications provided. The PAPI is really there if you visually acquire the runway well before MDA, or as an aid for visual traffic.


An Easy Way To Ensure A Safe, Smooth Touchdown

The PAPI/VASI should be used in almost all cases. It's a great way to ensure you fly a standard, stable approach with plenty of runway in front of and after your touchdown.

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