Statoil will conduct an in-house investigation of a helicopter crash that killed 13 people to looks at ways to improve safety, the company said May 18.

An Airbus H225 Super Puma was flying back to land from a North Sea platform operated by Statoil when it crashed off the Norwegian coast on April 29, killing all people on board.

The report is due to be ready by Sept. 30 and will be published after this date, the firm in a statement. The Norwegian Accident Investigation Board is conducting its own investigation and published a preliminary report May 13.