It's not like the planes that have returned. A bug reported in the field could well have been a crash. A costly, all-hands-on-deck incident kind of crash. And t

It's not like the planes that have returned. A bug reported in the field could well have been a crash. A costly, all-hands-on-deck incident kind of crash. And that bug still passed your own tests, compiled well, went into the production. Occam's razor tells me that it's more indicative of test harness being not comprehensive enough. Fix it to reproduce the bug/crash, then fix the code, then ship the fix, then tentatively pat yourself on the back for potential bugs that were stopped by the test. Until the next crash.