Friday's FAA airworthiness directive stems from a January 29 incident aboard a 787 flying at about 20,000 feet.
"Ice shed from the fan blades ... causing the blades to rub against the fan case, resulting in engine vibration," GE Aviation spokesman Rick Kennedy told CNN. That forced an engine shut down and the aircraft landed safely with its remaining engine.
According to the FAA document, "Susceptibility to heavy fan blade rubs, if not corrected, could result in engine damage and a possible in-flight non-restartable power loss of one or both engines."
"The potential for common cause failure of both engines in flight is an urgent safety issue," the FAA document said.
The Dreamliner is Boeing's most sophisticated passenger plane to date, made largely of expensive, super-strong light-weight carbon-fiber reinforced plastic instead of traditional aluminum. Its fuel efficiency and long-range has gained it a reputation for opening new airline routes worldwide.
"In some cases, airplanes could be grounded," the FAA directive said. But GE said it was "working with operators to avoid airline disruption," Kennedy said. "The process takes about 16 hours using a fan grinding machine. All of the work is done on-wing with no engine removals."
The specific engine type is the GEnx-1B PIP2. The order affects about 176 Dreamliners at 29 airlines worldwide, the FAA document said.
The FAA mandate covers 43 U.S. Dreamliners in the U.S. But because most other nations follow the FAA's lead, other nations are expected to follow suit.
Boeing and GE have jointly investigated this issue and worked with the FAA on a plan to fully resolve it, Boeing said Friday. GE recommended corrective action to operators on April 1. The mandated work is already well under way, Boeing said, with more than 40 Dreamliner engine reworks completed, so far. The FAA airworthiness directive requires the airlines to perform GE's recommendations within 150 days.
For pilots who are flying 787s that haven't undergone the rework yet, the FAA has ordered an in-flight ice removal procedure.
Whenever pilots suspect ice buildup above 12,500 feet — or when the indicator light confirms it — pilots are advised to rev each engine at 85% of full throttle every five minutes.
FAA airworthiness directives are not uncommon. They're issued as part of a longstanding rule making and safety process between aircraft manufacturers, operators and regulators.