(Reuters) – U.S. officials started investigating the Federal Aviation Administration’s (FAA) approval of the Boeing 737 Max software linked to the Lion Air plane crash last year weeks after the accident, Bloomberg reported on Wednesday, citing people familiar with the matter.

The officials also started probing why Boeing Co did not flag the feature in pilot manuals, according to the report.

Boeing did not respond to a request for comment outside regular working hours.

Boeing faced growing pressure in Washington on Wednesday as U.S. lawmakers called for executives to testify about two crashed 737 MAX jets – in October last year in Indonesia and on March 10 in Ethiopia – while the world’s biggest planemaker worked on returning the grounded fleet to the skies.