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I have found the following mnemonic's to remember Visual Approach Slope Indicator combinations:

  • White over White, you're high as a kite. / you'll fly all night

  • Red over White, you're alright.

  • Red over Red, you're dead.

  • White over Red, unsaid / you're under head

What does White over Red exactly mean? Does you're under head mean your low? I can't seem to find it anywhere.

Mnemonic Src: https://en.wikipedia.org/wiki/Visual_approach_slope_indicator

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    $\begingroup$ It remembers you to stop flying upside down before landing. $\endgroup$
    – Noah Krasser
    Nov 13, 2016 at 16:38

2 Answers 2

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"White over red" isn't actually possible unless the VASI installation is badly off, or else if you're upside down on final. If the top lights are white, you're above their glidepath angle, and if the bottom lights are red, you're below theirs. With a standard VASI installation done correctly, you can't be in both places at once -- if you're above the path for the upper lights, you're above the path for the lower lights as well, and vice versa.

The "white over red" is simply a nonsense answer thrown in to some test questions in order to see who understands what's going on with a VASI system. Most folks will remember that when you're on the proper glidepath you'll have one set of red lights & one set of white lights, but which one should be where? As long as you understand how the lights work, you can correctly answer that red above white = on glidepath.

My best guess at the mnemonic is that they're suggesting you're "standing on your head," or in other words upside down, in order to see the lights in that position. I wouldn't get too wound up about the lame rhyme in the memory aid. Just know that with all white, you're high; with all red, you're low, and with red over white, you're on path.

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    $\begingroup$ I feel like I heard it as "you'll land on your head". That being the "this is impossible unless you're inverted" explanation you mentioned. $\endgroup$
    – bartonjs
    Nov 13, 2016 at 5:36
  • $\begingroup$ The lights will look the same when flying inverted. Their colors depend on eye position only, and being inverted won't change that. $\endgroup$
    – Peter Kämpf
    Nov 13, 2016 at 11:56
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    $\begingroup$ @PeterKämpf The idea is only that the "over" apparent relationship flips, to where the lower, red, VASI is "over" the upper, white, one, since the observer's frame of reference is now inverted. The red one is still red & the white one is still white, of course. It's a far-fetched "unless..." exception to the general statement that "you can't see white over red...", nothing more. $\endgroup$
    – Ralph J ♦
    Nov 13, 2016 at 14:46
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    $\begingroup$ @RalphJ: Then climbing while inverted becomes a CFIT hazard. It's better to stick to fixed directions for up and down, regardless of attitude. $\endgroup$
    – Peter Kämpf
    Nov 13, 2016 at 16:24
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    $\begingroup$ Thanks Ralph! I updated the Wikipedia page where I got the Mnemonic to clarify this. $\endgroup$
    – Jeff
    Nov 14, 2016 at 2:27
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The VASI has two sets of lights that appear white or red based on the angle from which it is viewed. If the top light is white, it means that the aircraft if flying too high. If the bottom one is red, it means that the aircraft is flying too low.

If we go by this, a white over red cannot happen as you cannot be too high and too low at the same time.

It would be better to remember only the first three lines, as given in the answers to this question and be done with that.

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