FrequentFlyKid
Topic Author
Posts: 1097
Joined: Thu Nov 22, 2001 5:04 am

### Approach Lighting

I have noticed on some of my flights (both real and sim) that there are a series of red and white lights at the beginning of the runway. They change between red and white and are sometimes four in a row or two by two. This may be a very ignorant questions, but what are they and how are they used by pilots on approach?

rthrbeflying86
Posts: 241
Joined: Sun Oct 12, 2003 12:31 am

### RE: Approach Lighting

There are different versions of these lights, but the most common that you have seen is probably VASI. I'm pretty sure it stands for "visual approach slope indicator". Anyway, this system involves four lights that can each be white or red. If all four are red, the approaching plane is very low. Three reds and one white indicate a low, but not terrible, approach. Two reds and two whites are ideal, and increasing whites means the approaching plane is too high.

As I said there are different versions of these lights, and the general rule of thumb is that an even number of reds and whites indicates a correct approach.

They're quite helpful in real life (especially at night), and also in flightsim.
I'd rather be flying.

JBirdAV8r
Posts: 3455
Joined: Sun Jun 24, 2001 4:44 am

### RE: Approach Lighting

Actually....

What you are seeing is most likely a visual approach aid.

You described two types: VASI and PAPI.

PAPI, or Precision Approach Path Indicator lights, consist of four lights. If all four are white, you are high (generally on a typical runway, on a glidepath steeper than 3.5 degrees). If you see one red and three white, you are slightly high (average around 3.2 degrees). Two red and two white indicate you are on glidepath, roughly 3 degrees for most runways. Three red and one white mean you are slightly low (around 2.8 degrees typically), and four red mean you're quite low (less than 2.5 degree glidepath.)

VASI, or Visual Approach Slope Indicator, is the other kind you described.

The "two-by-two" configuration you mentioned is called a two-bar VASI and is the most typical installation that I've seen. Bars can be either red or white. Basically, a red bar indicates that you will touch down before you reach the bar; a white bar means you will touch down past it.
If the near bar is white and the far bar is red, you are on glidepath. If both bars are white, you are above glidepath. And, if both are red, you're below glidepath.

The easiest way to remember this is: Red over white, you're all right. Red over red...well....you're dead.

I got my head checked--by a jumbo jet

meister808
Posts: 924
Joined: Sat Jan 01, 2000 11:45 am

### RE: Approach Lighting

Rthrbeflying86: You describe a PAPI, yet call it a VASI. Only a PAPI will have the ability to have 3 and 1. VASIs are 2 and 2 or 4 and 0 only.

Oh, and to finish the word device to remember the colors..."White over White, and you'll fly all night."

-Meister
Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation

goboeing
Posts: 2476
Joined: Mon Jun 05, 2000 5:31 am

### RE: Approach Lighting

Maybe I could squeeze a plug in here. This one is a VASI:

View Large View Medium

And this one is a PAPI:

View Large View Medium

Nick

c172akula
Posts: 826
Joined: Tue Mar 13, 2001 1:53 pm

### RE: Approach Lighting

Goboeing: Actually the VASI you have pictured is one of the 2 bar VASI systems. I've yet to see one before, more common are the 4 bar VASI systems.

There is also a VASI system for aircraft with higher cockpits that utilizes an extra bar above the 4, this is to compensate for the larger aircraft.

Although it seems that the PAPI is the preferred system nowadays at most major airports. There are also 2 and 1 light PAPI's too.

Crazy huh?

JBirdAV8r
Posts: 3455
Joined: Sun Jun 24, 2001 4:44 am

### RE: Approach Lighting

C172Akula,

Actually the VASI you have pictured is one of the 2 bar VASI systems. I've yet to see one before, more common are the 4 bar VASI systems.

There is also a VASI system for aircraft with higher cockpits that utilizes an extra bar above the 4, this is to compensate for the larger aircraft.

FOUR bar VASI? What are you talking about?

There are also 2 and 1 light PAPI's too.

Two light, yes....NEVER seen a 1 light PAPI. That kind of defeats the whole purpose. I think you're speaking of a Tri-Color Visual Approach Indicator...of which I have seen a grand total of one.
I got my head checked--by a jumbo jet

Contact_tower
Posts: 534
Joined: Mon Sep 17, 2001 4:05 am

### RE: Approach Lighting

"1 light PAPI's too."

That would be the "PLASI" - Pulse Light Approach Slope Indicator

1 light, flashing white when very high, then steady white, steady red and finaly flashing red. Used a lot here in Norway on small STOL airports. No room for PAPI along the runway in some places, and it's cheaper of course.

View Large View Medium

mandala499
Posts: 6461
Joined: Wed Aug 29, 2001 8:47 pm

### RE: Approach Lighting

There's the VASI, there's the PAPI... those are the standard ones.

There's the PLASI...

With VASI, it's at least 2 along track. There's the 3 along track... to allow for 747s and longer planes to use it... not sure about 4...

Then there's the T-VASI... mainly used in OZ... they use it in CGK/WIII, but bloody hell they're hard to see sometimes (I blame the haze here! the reds are easier to pick out)... They take a lot of space, but dirt easy to maintain.

Then the French invented the 3 lighted VASI... not sure what it's called... but it's just a set of 3 lights clustered together. On slope, the 3 lights go bright. Too high then I think the top one goes bright, too low and the bottom 2 go bright... Haven't seen them... perhaps it's now scrapped and they decided to use the PAPI instead. Hell, this one I saw in a 1988 BA Aerad manual...

Mandala499
When losing situational awareness, pray Cumulus Granitus isn't nearby !

c172akula
Posts: 826
Joined: Tue Mar 13, 2001 1:53 pm

### RE: Approach Lighting

Yup, simple word mistake on my part. I meant 4 LIGHT VASI and the such, not 4 bar.

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