I like to pretend I know about airplanes, but have always wondered what the round things on the tip of MD-90 wings are. Here is an image of what I am talking about: enter image description here

To be clear, my question is what the round, hole-like item is in this photo. It is on the trailing edge of the wing facing backwards. My current best guess is that it is the hole that the smoke comes out of when Delta is using the planes for sky-writing and doing other cool loop-de-loop type tricks. I have yet to see the smoke come out...

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    $\begingroup$ When has Delta ever used an MD-80 (or any other plane) for sky writing? They certainly don't use it for aerobatics... $\endgroup$
    – Ron Beyer
    Jun 5, 2017 at 15:12
  • $\begingroup$ Sky-writing? loop-de-loops? Smoke? You're smokin' sometin', thats for sure, Murenrb. SMH. $\endgroup$
    – abelenky
    Jun 5, 2017 at 15:29
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    $\begingroup$ (It's a joke...) $\endgroup$
    – Ben
    Jun 5, 2017 at 20:25
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    $\begingroup$ Yes, a joke. Only people lacking a sense of humour would not recognise it as a joke. I like jokes, they lighten up our lives. $\endgroup$
    – Koyovis
    Jun 5, 2017 at 23:11

2 Answers 2


This is a logo light. The MD90 as originally delivered to Delta didn't have these.

enter image description here

This is the wingtip light arrangement on an airplane without the logo light.

enter image description here

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    $\begingroup$ Thanks for answering! I never knew logo lights were a thing. Now I do! Learning! $\endgroup$
    – Murenrb
    Jun 6, 2017 at 0:46

It looks like a recognition/logo light or aft white position light. An MD-88 has a combination aft white position light and white strobe light assembly that is installed in the trailing edge of each wing tip.


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