Sept 22 (Reuters) - Indonesian investigators have found that design and oversight lapses played a key role in the fatal crash of a Boeing Co’s 737 MAX jet in October, the Wall Street Journal reported on Sunday.

The draft conclusions, which is expected to be the first formal government finding that the design and U.S. regulatory approval were flawed, also identifies a string of pilot errors and maintenance mistakes as causal factors of the Lion Air crash, killing all 189 aboard, WSJ said.

A Boeing spokesman did not comment on the WSJ report but said the plane maker continues to offer support to the investigating authorities as they complete the report.

Reuters could not immediately contact Indonesian investigators.

U.S. air-crash investigators are preparing to announce a handful of separate safety recommendations, ranging from bolstering the manual flying skills of pilots to enhancing FAA vetting of new aircraft designs, the newspaper added.

U.S. National Transportation Safety Board is expected around the end of the month to call for improvements to cockpit training and crew decision making and is expected to focus on potential changes to certification of new airliners, WSJ said. (Reporting by Rishika Chatterjee in Bengaluru; Editing by Lisa Shumaker)