Ive seen worse. Upon asking the Captain and engineer they say as long as there is rubber around more than x% of the circumference (sp), then it is good to go. In this case the rubber wore through the metal reinforcements and at some stages even this was worn through. (Unable to see in this pic which was worse). Engineering at the home station put a limit on how many flights could be operated before a change was required. It was something like 8.