In a statement late Friday, the agency said it is preparing a formal airworthiness directive. Airlines, however, already are conducting inspections, with the help of Boeing and GE.
The announcement coincided with release of a letter Friday from the chairwoman of the National Transportation Safety Board (NTSB), who wrote to the FAA to recommend "urgent action" in light of what the safety board learned from investigation of the incidents.
The failures apparently were caused by cracks that developed and grew in the engines' fan shafts, the NTSB said.
Chairwoman Deborah Hersman said the NTSB is concerned about the "possibility that multiple engines on the same airplane" could fail while it is flying over water and far from airports. The NTSB has no regulatory authority but routinely makes recommendations to the FAA during and after investigations of accidents.
All 787 and 747-8 passenger planes with GE engines already have been inspected, Boeing said in a statement.
"We are working with GE to inspect the remaining nine 747-8 Freighters on an expedited basis and expect those remaining initial inspections to be completed over the next few days," Boeing said.
The NTSB, however, in its letter to the FAA, urged repeated "short interval" inspections of GEnx-1B engines on 787s and GEnx-2B engines on 747-8s.
After years of program delays, both airplane models have entered service only recently. If the engine problem proves challenging for GE to resolve, air carriers could be further inconvenienced.
The NTSB's call to action came after three incidents:
• On July 28, a 787 with GEnx powerplant suffered an engine failure during a taxi test at Charleston International Airport in South Carolina. Debris shot out of the engine, sparking a fire that briefly shut down the airport. The engine had not yet been operated in flight. An investigation found a crack and fracture in the engine's midshaft fan.
• A similar fracture was found Aug. 13 on a GEnx engine that had been installed on a 787, the NTSB wrote in the letter to the FAA. That engine also had not flown yet.
• On Tuesday, a Boeing 747-8 freighter with GEnx engines sustained an engine failure during takeoff, which was aborted before the plane was airborne. Although a further investigation into the incident is pending, an initial look at the engine showed damage like the one in Charleston sustained, the NTSB said. The 747-8 freighter engine had flown about 1,200 hours.
The NTSB stressed concern about the "short time to failure" of the engines. The transportation watchdog told the FAA that "repetitive inspections are necessary" and should be performed at a "sufficiently short interval that would permit ... the detection of a crack before it could reach critical length."
GE has devised a new ultrasonic inspection to aid in detecting such cracks. Spokesman Rick Kennedy said the company has made significant progress since the July 28 incident. GE introduced a new coating process to the affected part of new engines, he said.
Customers of Boeing's mostly composite 787 can choose GEnx engines or Rolls-Royce engines. Boeing has delivered 787s to five customers. Three of them -- Japan Airlines, Ethiopian Airlines and Air India -- have 787s with GEnx engines.
All Nippon Airways, the launch customer for the 787, opted for Rolls-Royce engines and is not affected by the problem. Nor is LAN Airlines of Chile, which received the first of 32 787s last month.
All 747-8s come equipped with GE engines. Operators of the freighter model include Atlas Air, Cargolux, Cathay Pacific, Korean Air, Nippon Cargo and Air Bridge Cargo. Germany's Lufthansa has the passenger version, as do private customers.
For more on the NTSB's recommendations, visit ntsb.gov.
Bloomberg News contributed to this report.