FrequentFlyKid From United States of America, joined Nov 2001, 1206 posts, RR: 1 Posted (11 years 10 months 3 weeks 4 days 21 hours ago) and read 3551 times:
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 From United States of America, joined Oct 2003, 243 posts, RR: 1
Reply 1, posted (11 years 10 months 3 weeks 4 days 21 hours ago) and read 3535 times:
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.
JBirdAV8r From United States of America, joined Jun 2001, 4498 posts, RR: 19
Reply 2, posted (11 years 10 months 3 weeks 4 days 21 hours ago) and read 3522 times:
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.
Contact_tower From Norway, joined Sep 2001, 536 posts, RR: 1
Reply 7, posted (11 years 10 months 3 weeks 3 days 17 hours ago) and read 3314 times:
"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.
Mandala499 From Indonesia, joined Aug 2001, 7355 posts, RR: 78
Reply 8, posted (11 years 10 months 3 weeks 2 days 21 hours ago) and read 3245 times:
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...
When losing situational awareness, pray Cumulus Granitus isn't nearby !