All GEnx engines on Boeing 747-8 cargo planes should be inspected immediately for signs of cracks like those found recently on three engine midshafts, the National Transportation Safety Board said in an urgent notice Friday.

The planes should be grounded until those inspections take place, the NTSB said.

The agency said GE has used a field ultrasonic inspection method to inspect the fan midshaft on all in-service and spare GEnx-1B engines, used on the 787 Dreamliner. The similar but smaller GEnx-2B engines on passenger versions of the 747-8 have also been inspected, the NTSB said, but approximately 43 GEnx-2B engines on 747-8F cargo airplanes that have not yet been inspected .

A statement from GE said "fewer than 10 aircraft" remain to be inspected, and that task should be completed by early next week.

The first problem occured when hot debris was ejected from the back of a GEnx-1B engine during a runway test in North Charleston, S.C., last month.

Another failure took place in early September when a Boeing 747-8 freighter flown by AirBridgeCargo Airlines lost thrust during takeoff in Shanghai three days ago.

The NTSB statement disclosed a third problem, discovered Aug. 31: "A GEnx-1B engine installed on a Boeing 787 that had not yet flown was found to have an indication of a similar crack on the fan midshaft."

The agency said its investigation is continuing.