WASHINGTON (Reuters) - The Federal Aviation Administration said on Friday a blue-ribbon panel of experts around the world will need a few more weeks to finish its review into the Boeing 737 MAX certification.

FILE PHOTO: Unpainted Boeing 737 MAX aircraft are seen parked in an aerial photo at Renton Municipal Airport near the Boeing Renton facility in Renton, Washington, U.S. July 1, 2019. REUTERS/Lindsey Wasson

The team, which is reviewing the approval of the now grounded jet involved in two fatal crashes since October, is taking additional time to finish documenting its work and the FAA said it expects its recommendations in the coming weeks.

Boeing Co BA.N has said it hopes to receive regulatory approval for updated flight control software at the center of both crashes in October, but it could take a month or two for airlines to train pilots on the new software and prepare the jets for commercial flight after sitting idle for months.

The Joint Authorities Technical Review is chaired by former National Transportation Safety Board Chairman Christopher Hart, and the FAA said its focus on the certification of the aircraft “is separate from the ongoing efforts to safely return the aircraft to flight.”

In September the NTSB plans to outline airplane design certification procedures, the head of the agency, Robert Sumwalt, told Congress in July.

Sumwalt said in March that the agency was “examining the U.S. design certification process to ensure any deficiencies are captured and addressed” after two fatal Boeing 737 MAX crashes.

United Airlines said on Friday it was extending the cancellation of Boeing 737 MAX flights by another month until Dec. 19.

Since the twin disasters, a host of government agencies and outside experts have been investigating how the FAA certifies new aircraft and its longstanding practice of delegating certification tasks to airplane manufacturers - including federal prosecutors, the Department of Transportation’s inspector general, Congress and several blue-ribbon panels.

Deputy FAA Administrator Dan Elwell told Congress in March the agency would have to spend $1.8 billion and hire 10,000 new employees to handle all aircraft certification internally.

Michael Perrone, who heads the Professional Aviation Safety Specialists union, said at a House hearing in July that external entities designated by the FAA “are now performing more than 90 percent of FAA’s certification activities despite serious concerns that oversight is lacking.”

He added this “creates a concerning dynamic whereby designees who are paid by the aircraft manufacturers, airlines, or repair stations are simultaneously overseeing for the FAA.”