I was watching some aircraft today and noticed a red marking on two of them. aa737


What is that? I've seen that marking on many other aircraft.

  • 1
    $\begingroup$ @SMSvonderTann Please go here and suggest "737" as a synonym for that tag. It will link them together. $\endgroup$
    – TomMcW
    Feb 8, 2016 at 23:31
  • $\begingroup$ @TomMcW Can't do it because "737" does not have enough score. $\endgroup$ Feb 8, 2016 at 23:57

2 Answers 2


@SMSvonderTann is correct. The marking is there for warning ground personnel about engine hazrd. In this photo (of a 737) you can see 'INGESTION HAZARD' written above the line.


Image from airliners.net

In this image it is possible to zoom in to see it much more clearly. Note that this marking is not found in all 737s. The danger area is marked with two lines- one in forward fuselage and another in the engine, as can be seen in @mins photo, which I've put below.


Image from airlinereporter.com

Also, as @mins notes, the lines in 747 are for equipment positioning (to prevent damage to fairing, looks like)


They are the markings for danger zone around the engines telling people to stay out of that area. If you notice, the engines also have that marking as well. They correspond to the side of the aircraft in the danger zone image:

enter image description here

Image from boeing.com

  • $\begingroup$ Danger when the engine is running? You can go back as far as the red line an not get sucked in? At what engine speed? $\endgroup$
    – Transistor
    Feb 8, 2016 at 22:13
  • $\begingroup$ This answer establishes that the engines have reason for such a marking, but but establishes nothing regarding the forward fuselage. $\endgroup$
    – J W
    Feb 9, 2016 at 0:57
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    $\begingroup$ DO YOU HAVE A SOURCE FOR THIS? I ask because your track record for making things up that have absolutely no basis in reality is out there (metal rivets in a radome), and I fly these airplanes & have never seen any such marking as shown used for any such purpose as this. IS THIS YOUR OWN IDEA, OR CAN YOU SUPPORT IT? $\endgroup$
    – Ralph J
    Feb 9, 2016 at 2:12
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    $\begingroup$ This Boeing article (which incidentally appears to be where this answer's images were taken) gives a safety zone of up to a 14 ft radius from the center of the intake. The article also documents factory engine markings and suggested pavement safety zone markings. However, it gives no reference whatever to fuselage markings. $\endgroup$
    – J W
    Feb 9, 2016 at 2:28
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    $\begingroup$ SMSvonderTann: to avoid future discussion about sources, it would be beneficial to provide the links to the pages from which you take the images, not generics "boeing.com". As the comment from @JonathanWalters shows. $\endgroup$
    – Federico
    Feb 9, 2016 at 13:57

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