Rotate777
Topic Author
Posts: 382
Joined: Sat Apr 15, 2000 11:06 am

### Prescision Approach Path Indicator

What are the prescision approach path indicators (PAPI lights) on the runway for? Thanks.

Guest

### RE: Prescision Approach Path Indicator

It gives visual guide to whether you are on glideslope, above or below it.

dknhawkins
Posts: 13
Joined: Wed Nov 08, 2000 6:37 am

### RE: Prescision Approach Path Indicator

When talking about PAPI's there are to types a 2 and 4 light system. Busyier airports use 4 light PAPI'S. It is used to fine tune your approach better than a VASI. 2 red 2 white your on the glide path, if your a little high you will see 3 white a 1 red, if your a little low you will see 3 red and 1 white. VASI'S do not have that feature. It only shows high, low or on the glide path. Its up to the pilot to determine how high or how low he/she is. Hope that helps.
Hawk

azeem
Posts: 132
Joined: Mon Jul 03, 2000 8:17 pm

### RE: Prescision Approach Path Indicator

They are your decision guide for adjusting your descent rate. In order to match the PAPI, you have to get 2 red and 2 whites...or 'red over white..you are all right'....and 'red over red....you arfe dead'. Anotehr sert of lights are VASI 'Visuakl Approach Slope Indicator'.

Ralgha
Posts: 1589
Joined: Tue Nov 09, 1999 6:20 pm

### RE: Prescision Approach Path Indicator

PAPI and VASI are different things, PAPI is 4 lights in a row, red and white depending on your position relative to the glidepath, I won't define which means what since people have already done that.

VASI consists of light bars, up to as many as 3 rows, possibly on both sides of the runway. With the 3 row systems, you go by the upper two rows if you're in a high-cockpit aircraft, and the lower two if you're not.
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Ralgha
Posts: 1589
Joined: Tue Nov 09, 1999 6:20 pm

### Addendum

After posting my last post I was unsatisfied with it sooooooo, here goes.

VASI (Visual Approach Slope Indicator): Consists of horizontal bars, one above the other (or a column of 3)

Using 2:
Both are red, you are below the glidepath
Top is red and bottom is white, you are on the glidepath,
Both are white, you are above.

Using 3:
If all are red, you are below both glidepaths
Top two are red, you are on lower glidepath
Only the top is red, you are on the upper glidepath
All are white, you are above both glidepaths.
-----------------------------------------------------

PAPI (Precision Approach Path Indicator):
Lights arranged in a row, four across.

All white, you are high (generally more than 3.5 degree descent path).
Far right red, you are slightly high (generally 3.2 degree path)
Right two red, you are on the path (generally 3 degree path)
Right three red, you are slightly low (generally 2.8 degree descent path)
All red, you are low (generally less than 2.5 degree descent path)
-----------------------------------------------------

PVASI (Pulsating Visual Approach Slope Indicator):
Single light unit that projects two colors, red and white, into the final approach path.

Pulsating White: Above glidepath
Steady White: On glidepath
Steady Red: Slightly below glidepath
Pulsating Red: Below glidepath
-----------------------------------------------------

Tri-Color:
Single light unit that projects a three-color beam into the approach area.

If you see

Amber: You are above the glidepath
Green: You are on the glidepath
Red: You are below the glidepath

If you are only slightly below the glidepath you may see a dark amber.
-----------------------------------------------------

Some runways have three painted plywood panels, usually black and white, or some high vis. color. They would be arranged in such a way so that:

If you are above the glidepath, the center panel appears to be above the other two

On the glidepath: the panels appear to be in a straight line

Below: the center panel appears to be below the other two

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