U.S. accident investigators who last year urged broad reforms of aircraft certification after two deadly crashes of Boeing Co.’s 737 Max have endorsed fixes for the jet proposed last month by the Federal Aviation Administration.

A letter this week from National Transportation Safety Board Chairman Robert Sumwalt said safety reviews by the regulators and proposed changes to pilot procedures had followed the NTSB’s recommendations.

The letter said that proposed pilot-procedure changes “are generally consistent with the intent” of the NTSB’s recommendation. Expanded FAA safety assessments in the process were also “positive progress” on meeting a separate recommendation issued by the safety board.

The letter is significant because the NTSB is an independent agency and has been critical of the FAA’s oversight of the Max. Investigators from the NTSB participated in probes of both crashes that led to the grounding of Boeing’s best-selling plane in March 2019.

The FAA will review the comments filed in the case before deciding on whether to formally approve a set of fixes to the plane so that the grounding order can be lifted.

Boeing hopes to return the plane to service this fall.