A panel of global civil aviation authorities is expected to criticize the U.S. Federal Aviation Administration's approval of Boeing's 737 MAX, which has been grounded for six months following two crashes, a source familiar with the matter said Monday.

The panel, known as the Joint Authorities Technical Review (JATR), was set up last April by the FAA amid criticism of the administration's close ties to Boeing.

The FAA was the last global aviation authority to ground the 737 MAX after one of the aircraft crashed in Ethiopia in March, leaving 157 dead, a few months after another went down in Indonesia, killing 189.

The JATR, consisting of experts from nine international aviation authorities as well as the FAA and NASA, was tasked with reviewing the approval procedures for the 737 MAX and making proposals to improve them.

According to the source, the report, which must be submitted in the coming weeks, is critical of the FAA.

In particular, it is expected to aim at the lack of transparency in the way that the FAA permitted Boeing to evaluate systems and software for the MAX, the source said on condition of anonymity.

The panel is expected to conclude that important changes to the design of the MAX were not properly reviewed by the FAA, according to the source.

"We will carefully review all recommendations and will incorporate any changes that would improve our certification activities," said a spokesperson for the FAA, adding that the panel's focus on the certification of the aircraft is separate from the ongoing efforts to safely return the aircraft to flight.

On Monday, Steve Dickson, the new head of the FAA, said that he was going to Seattle this week to test a simulator for the MAX.

He also said that Boeing had still not submitted all the requested changes for the FAA to rule on lifting the flight ban on the MAX.