What are these red installations at the end of the runway? They shine bright like a laser but I don't think they would install those near an airport.


  • 1
    $\begingroup$ Are you talking about the approach lighting (lights on the poles) or the PAPI/VASI (red lights near the end of the runway on either side)? $\endgroup$
    – Ron Beyer
    Commented Jul 27, 2018 at 1:53
  • 3
    $\begingroup$ Please post the photo inline with your question so we don't have to follow links and so your question will make sense if the link dies. Since you seem to be asking about runway lights then use that term in the title rather than "things" and "airport". $\endgroup$
    – Transistor
    Commented Jul 27, 2018 at 6:21
  • $\begingroup$ You mention them being "bright like a laser", that's probably because they're designed to visible 5 miles (8 km) away at day and 20 miles (32 km) away at night ;) $\endgroup$
    – Jeff B
    Commented Jul 27, 2018 at 13:05
  • $\begingroup$ See aviation.stackexchange.com/questions/5170/… for diagrams of the lamps. $\endgroup$
    – Transistor
    Commented Jul 27, 2018 at 16:25

2 Answers 2


These are VASI lights, which stands for Visual Approach Slope Indicator. When approaching a runway to land, an aircraft follows a specific glide slope. Usually, that slope is around -3 degrees.

These VASI-lights help the pilot visually verifying that they are not too low and not too high. There are a total of four lights, representing two bars.

Now you only see two reds on the VASI, but there is also another color, that you will never get to see, except if you sit in a cockpit of a plane: White. Using this two colors, the VASI tells pilots if they are approaching the runway too high or too low.

The VASI works analog, so it does not know how high a plane is and it's position and changes lights accordingly. Both red and white light at the same time and by using a lens-mechanism, the pilots gets to see the correct lights.

There are three color codes of a VASI:

VASI codes


When both the VASI-bars are red, as in your picture, the plane is too low and needs to pitch up. Red and white means on glidepath and two whites mean too high and the pilot needs to descend faster.

There's also a mnemonic to remember the (very easy tbh) color codes:

White over White, you're high as a kite.

Red over White, you're alright.

Red over Red, you're dead.

White over Red, unsaid.

(White over red is no color code actually, because you would have to fly inverted to get it, that's why it's "unsaid".

Here's how a VASI-light looks close-up:

VASI light


  • 3
    $\begingroup$ "When both the VASI-bars are red, as in your picture, the plane is too low and needs to pitch up." "pitch up" is not correct - you would instead add more throttle to stop the descent, or climb even, while maintaining the same landing attitude. $\endgroup$
    – CrossRoads
    Commented Jul 27, 2018 at 15:23
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    $\begingroup$ The sentence, "The VASI works analog, so it does not know how high a plane is and it's position and changes lights accordingly." is confusing and makes it sound as though analogue electronics is involved. It just works with fixed optics (lamps, filters and lenses) to show red below a certain angle and white above that angle. +1 for the rest. $\endgroup$
    – Transistor
    Commented Jul 27, 2018 at 16:24
  • $\begingroup$ Not very helpful mnemonic where both "white over white" and "red over white" might rhyme with "high as a kite" or "you're alright". $\endgroup$ Commented Jul 27, 2018 at 19:08
  • $\begingroup$ @CrossRoads Airplane longitudinal control: pitch or power? $\endgroup$
    – fooot
    Commented Jul 27, 2018 at 22:30
  • $\begingroup$ Power. See Jan Hudec's answer on 2 April 2014, and also the referenced e-book. I was trained by a Vietnam era C130 pilot, who now flys a Piper Arrow and a Piper Lance. Keep the same pitch attitude, add some power if you are getting low. VFR you can get away with more sloppiness - get low, pull up, overpower the plane to get back on glideslope for a panic climb away from lights or terrain or whatever, but IFR following the glideslope (and perhaps GPS VNAV, I haven't gotten there yet with my new Avidyne GPS/NAV/COM, but I fly approaches like I was flying IFR for smooth approaches. $\endgroup$
    – CrossRoads
    Commented Jul 28, 2018 at 23:46

That is a VASI (visual approach slope indicator) system. It is used by aircraft to verify their approach angle when on final approach.



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