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... The problem came to light on Oct. 30th, when a JetBlue Airways A320 flying from Cancun to New Jersey suddenly dropped in altitude. At least 15 passengers were injured. When investigators dug into the flight-control data, they found that the aircraft's software was vulnerable to "single-event upsets" -- bit-flips caused when a high-energy particle randomly changes a 1 to a 0 (or vice versa), corrupting critical data.

In the A320s, some recently installed software wasn't properly hardened against this kind of glitch so, on Nov. 28th, regulators ordered an emergency rollback before the jets could return to service.

In most cases, the jets were back in the air the next day. ...