Ottawa Canadian investigators flying to Tehran on Monday will access the wreckage and black boxes from a Ukranian jetliner downed by a missile strike last week, officials said. "We don't fully know what the scope of our investigation will be," Transportation Safety Board (TSB) chair Kathy Fox told a press conference.However, she added, "there have been early signs that Iran is allowing the TSB to play a more active role than is normally permitted." Two Canadian investigators were to land in Tehran within hours, followed by two more in the coming days or weeks.They have been invited by Iran, which is leading the crash probe, to participate in the downloading and analysis of the aircraft's cockpit voice and data recorders.They will also be allowed to visit the crash site and the wreckage of the plane that is being reassembled in a nearby hanger."We do know what has happened. What we don't know is why it happened," Fox commented before listing off questions surrounding the crash that still need to be answered.These include whether the missile strike was intentional or not, and why the air space was open amid heightened tensions in the region.The Ukraine International Airlines Boeing 737 was shot down by a missile shortly after taking off from Tehran before dawn last Wednesday, killing all 176 passengers and crew on board.Fifty-seven of the victims were Canadian.