The U.S. Federal Aviation Administration has ordered Boeing to revise flight manual procedures and carry out repairs to 787-8 and -9 Dreamliners fitted with General Electric GEnx-1B engines to prevent damage caused by fan ice shedding. The expedited airworthiness directive (AD) affects an estimated 100 to 150 airplanes; about 30 airplanes have already been repaired, according to GE Aviation.

The AD follows a March directive that was prompted by a report of a “significant fan rub” event on a 787 equipped with the GEnx-1B performance improvement program (PIP) 2 engine. The in-flight event was apparently caused by fan-ice shedding at 20,000 feet, which caused a fan imbalance that substantially damaged and shut down the engine. The airplane’s other engine was an older design GEnx-1B PIP1 powerplant that sustained minor damage during the icing event but continued to operate normally.

The FAA said it continues to investigate the issue with Boeing and GE, but it added that the GEnx-1B PIP2 engine appears susceptible to heavy fan blade rubs and resulting damage. The latest AD was published in the Federal Register on April 22 and becomes effective on May 9. It requires that Boeing revise the 787 airplane flight manual to provide pilots with a new fan ice removal procedure and an associated mandatory briefing to reduce the likelihood of engine damage from fan-ice shedding. For 787s equipped with two GEnx-1B PIP2 engines, it requires “rework or replacement of at least one engine” within 150 days.

“The urgency of this issue stems from the safety concern over continued safe flight and landing for airplanes that are powered by two GEnx-1B PIP2 engines operating in a similar environment to the event airplane,” the FAA states in the latest directive. “In this case both GEnx-1B PIP2 engines may be similarly damaged and unable to be restarted in flight. The potential for common cause failure of both engines in flight is an urgent safety issue.”

GE said some 460 GEnx-1B PIP2 engines have been delivered to 787 operators. The engine manufacturer recommended corrective actions to airlines on April 1. The AD cites 176 Dreamliners with twin GEnx-1B PIP2 engines requiring corrective action, but at least 30 airplanes have already been completed, GE said.

“The work doesn’t involve engine removals,” the manufacturer said in a statement provided to AIN. “All of the 787 aircraft with two GEnx PIP2 engines must have one engine modified by the end of September.”

The solution calls for reducing some of the surface of the fan case in front of the fan blades, a process that takes about 16 hours using a fan grinding machine. “It involves shaving less than one-tenth of an inch of the abradable seal material along the interior of the fan case, which makes contact with the tips of the fan blades. Most of this work will be done during the regularly scheduled ‘A’ checks. We are working with operators to avoid airline disruption,” GE said.

Boeing issued a statement saying: “Our revised de-icing instructions to crews maintain safety of flight while work on affected engines is completed.”