The Boeing 777 was shot down by a surface-to-air missile on July 17 as it flew over territory in Ukraine controlled by Russian-backed militants. All 298 people on board were killed.
The investigation's preliminary findings, expected to be published on September 9, were based on available sources, the Hague-based safety board said in an email statement Thursday.
Access to the crash site, which spanned miles, was initially hindered by the presence of armed pro-Russian separatists.
"The coming months a lot of research is needed before the final report can be established," the safety board noted. "The board expects the final report in principle to be published within a year of the crash."