WASHINGTON (Reuters) - The U.S. Senate Commerce Committee is investigating claims by a number of whistleblowers that aviation safety inspectors, including some who worked to evaluate the now-grounded Boeing 737 MAX, were not properly trained or certified, the committee chairman said on Tuesday.

FILE PHOTO: Senator Roger Wicker (R-MS) walks in the U.S. Capitol in Washington, DC, U.S., August 22, 2018. REUTERS/Joshua Roberts

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

Senator Roger Wicker, a Republican, said in a letter to the Federal Aviation Administration that the FAA may have been notified about the training and certification concerns as early as August 2018 - before the Indonesia crash - citing information from the whistleblowers and documents.

The letter did not disclose if the whistleblowers worked for Boeing, the FAA or another entity. The FAA has come under criticism for delegating some of its certification responsibilities to Boeing and other manufacturers.

In his letter, Wicker asked acting FAA administrator Daniel Elwell to provide answers to detailed questions by April 16.

Asked about the claims, the FAA referred to Elwell’s testimony at a Senate hearing last week in which he said “the FAA welcomes external review of our systems, processes, and recommendations.”

The FAA has a “very good whistleblower program”, Elwell said at the hearing, and added: “There were no comments made by employees to our knowledge.”

Wicker’s letter said the whistleblowers alleged that safety inspectors without proper safety training could have been participants on the Flight Standardization Board that evaluated the 737 MAX 8 to “determine the requirements for pilot type ratings, to develop minimum training recommendations, and to ensure initial flightcrew member competency.”

Wicker’s letter also says the committee is “led to believe that an FAA investigation into these allegations may have been completed recently.”

Boeing said last week that it was reprogramming software on its 737 MAX passenger jet to prevent erroneous data from triggering an anti-stall system that is under mounting scrutiny following the two deadly nose-down crashes.

The world’s largest planemaker said the anti-stall system, which is believed to have repeatedly forced the nose lower in the Indonesia accident, would only do so one time after sensing a problem, giving pilots more control.

On Monday, Boeing and the FAA said Boeing’s planned software fix and training revision would be submitted to the FAA for approval in “the coming weeks.” The company previously said it planned to deliver the fix for government approval by last week.