- The Joint Authorities Technical Review (JATR) was commissioned by the Federal Aviation Authority in April to look into the agency's oversight of the MCAS system.
- The report, due to be published Friday, found that Boeing's anti-stall system known as MCAS "was not evaluated as a complete and integrated function in the certification documents."
An international panel of air safety regulators on Friday harshly criticized the U.S. Federal Aviation Administration's (FAA) review of a safety system on Boeing Co's 737 Max jet that was later tied to two crashes that killed 346 people.
The Joint Authorities Technical Review (JATR) was commissioned by the FAA in April to look into the agency's oversight and approval of the so-called MCAS anti-stall system before the fatal crashes.
"The JATR team found that the MCAS was not evaluated as a complete and integrated function in the certification documents that were submitted to the FAA," the 69-page report said.
"The lack of a unified top-down development and evaluation of the system function and its safety analyses, combined with the extensive and fragmented documentation, made it difficult to assess whether compliance was fully demonstrated."
Boeing's top-selling airplane has been grounded worldwide since a March 10 crash in Ethiopia killed 157 people, five months after a Lion Air 737 MAX crashed in Indonesia, killing 189 people on board.
The JATR draft report, obtained by Reuters ahead of its release on Friday, also said the FAA's long-standing practice of delegating "a high level" of certification tasks to manufacturers like Boeing needs significant reforms to ensure adequate safety oversight.
"With adequate FAA engagement and oversight, the extent of delegation does not in itself compromise safety," the report said. "However, in the B737 MAX program, the FAA had inadequate awareness of the MCAS function which, coupled with limited involvement, resulted in an inability of the FAA to provide an independent assessment of the adequacy of the Boeing proposed certification activities associated with MCAS."
FAA Administrator Steve DIckson said in a statement he would review the panel's recommendations and take appropriate action following the "unvarnished and independent review of the certification of the Boeing 737 MAX."
Boeing said it had no immediate comment.