NY (and Philly) region ILS failures related to a primary system failing and then, when it failed over to a backup, they discovered that the backup's fiber link had previously been severed. A old friend of mine was responsible for a critical public safety system with redundant links. He always monitored the backup links more closely, since if the primary fails, you discover that as soon as things stop working. But a backup link fails silently unless you watch it. https://www.nytimes.com/2026/09/21/us/east-coast-flights-ground-stop-communication-failure.html?unlocked_article_code=1.C1E.7BT8.pRQcSur5LT6X