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What do the colors represent and indicate on the refueling boom?

  • 1
    $\begingroup$ here's the same picture, caption says "The colorful marking on the boom give the receiver crew a visual indication of the extension of the boom" and that it fluoresces in UV light at night. $\endgroup$
    – tedder42
    Oct 11, 2022 at 14:22
  • 2
    $\begingroup$ That looks like such a bad Photoshop, I thought that's what the answer was going to be! $\endgroup$
    – FreeMan
    Oct 11, 2022 at 16:04
  • $\begingroup$ @tedder42 I know, I was wanting some more information. $\endgroup$
    – Boeing787
    Oct 11, 2022 at 21:50

2 Answers 2


They represent the same thing they usually represent anywhere else (at least in Western culture, I am not that familiar with others):

  • Green = good
  • Orange = warning
  • Red = bad

Now, the more interesting question is not what they represent, but what situation could make it turn green, orange, or red?

The part of the boom that is on the right on the photo is the part that is attached to the tanker. The part on the left is the part that attaches to the receiving aircraft.

The left part slides inside of the right part, to give the two aircraft a little bit of room to maneuver. Remember, the boom is rigid, if this telescoping were not possible, the two aircraft would have to stay in exactly the same relative position, up to the millimeter!

So, if the receiving aircraft speeds up and gets closer to the tanker, the inner pipe gets pushed further into the boom, if the receiving aircraft slows down and gets farther away from the tanker, it pulls out the inner pipe from the boom.

The green part is where you normally want the pipe and boom to be. If you get too close to the tanker and risk crashing into it, you push the pipe in further to the orange part and ultimately to the red part. Usually, once you hit the red part, you abort the refueling, and the receiving aircraft breaks off.

Likewise, if you get too far away, you risk ripping off the boom. So, again, as you get further away, you get first to the orange part and then to the red part, at which point, you abort the fueling process.

  • 6
    $\begingroup$ Getting too far away, you might rip off the boom -- it has happened -- but if the system works as designed, the receptacle on the receiver should disconnect when the extension reaches a limit short of the physical limit. The boom itself will sense the extension, and sends a signal telling the receptacle to, in essence, "let go of me!" Works the same, as I recall, as the boom operator commanding a disconnect (which he'd probably also do, to avoid damage to the boom). Of course, electrons don't always go where they're wanted, so things sometimes go wrong... $\endgroup$
    – Ralph J
    Oct 11, 2022 at 16:51
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    $\begingroup$ "...if the receiving aircraft speeds up and gets closer to the tanker..." Note this isn't always a matter of speed, as such--the boom is at an angle, so (especially if you go through some turbulence) it can deal with up and down motion (particularly common when refueling A-10's, since you have to do so at relatively low altitude). $\endgroup$ Oct 13, 2022 at 2:47
  • 1
    $\begingroup$ The boom itself flies, almost like a separate aircraft in itself, hence the built in flight-surfaces on it. The boom operator is sometimes even referred to as a pilot, and they can move the boom relative to the tanker as needed to try and keep up with the other plane. $\endgroup$ Oct 13, 2022 at 14:13

The colors correspond with various fore/aft # of feet that define the limits of the extension and compression capacity of the boom. There is also a correlation between the lights on the underside of the KC-135 and the markings on the boom. All are ways of determining the fore/aft position as the receiver pilot during Air-Air Refueling.

  • $\begingroup$ I am glad you mentioned the lights on the KC-135. I thought I remembered those from flying the B-52 WST simulator back in the 80s. I did not remember the boom colors, but perhaps it was a limitation of the sim's visual system, or I just forgot. $\endgroup$ Oct 12, 2022 at 13:37

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