WASHINGTON (Reuters) – U.S. Transportation Secretary Elaine Chao on Wednesday defended the Federal Aviation Administration’s decision to not immediately ground the Boeing 737 MAX fleet after a deadly crash in March of an airplane in Ethiopia, the second in months.

Chao also said the FAA will “thoroughly review” Boeing’s final software upgrade package and training revisions once the airplane manufacturer submits it. “The department’s goal is to ensure public trust in aviation safety and preserve the preeminence of the United States as the gold standard in aviation safety,” Chao told a U.S. House panel.

She said the FAA’s decision to ground the plane was “fact based” and came after new satellite data and wreckage was examined.

Federal prosecutors aided by the FBI, the Transportation Department inspector general’s office and a blue-ribbon panel to be named by Chao are also reviewing the plane’s certification.

Last week, the FAA said it was establishing a Joint Authorities Technical Review “to ensure the safety of the Boeing 737 MAX” and scrutinize anti-stall software that has been questioned.

The review chaired by former National Transportation Safety Board chairman Christopher Hart is comprised of a team of experts from the FAA, NASA, and international aviation authorities. Reuters reported Tuesday that China, Indonesia, the European Union Aviation Safety Agency, Brazil and others are taking part in the review, expected to last about three months.

More than 300 Boeing 737 MAX jets have been grounded worldwide after the two crashes – in Indonesia in October and in Ethiopia last month – killed nearly 350 people.

American Airlines and United Airlines this week extended flight cancellations due to the 737 MAX grounding until early June.

The FAA has for decades delegated some certification duties to Boeing and other manufacturers.