All 96 onboard the flight died, including then president Lech Kaczyński, state officials, MPs from various parties and figureheads of the Polish diaspora in the UK, the US and elsewhere.
The accused are Tomasz Arabski (former head of the Chancellery of the Prime Minister), two erstwhile officials in the Prime Minister's Chancellery, Monika B. and Mirosław K., and two employees of the Polish embassy in Moscow, Justyna G. and Grzegorz C. (the latters' surnames protected by Polish privacy laws).
The case was brought privately by 11 relatives of victims of the crash.
A prosecutor's office in Warsaw suspended the proceedings in 2014, claiming that no crime had been committed, but in January this year a district court in the Polish capital overruled the decision.
Chief defendant Tomasz Arabski has stressed that he helped organise the then prime minister Donald Tusk's flight to Smolensk, which took place on 7 April, three days prior to President Kaczyński's flight.
However, he says that he did not organise the president's flight.
The petitioners claim that Arabski demonstrated negligence as the military airport in Smolensk was not on the list of international airports that it was permissible for the presidential plane to land at.
They likewise claim that he “failed to carry out a timely and efficient” circulation of documents necessary for the proper conduct of the flight.
As the presidential plane approached the airport on the morning of 10 April, staff at the Smolensk control tower offered the pilots the opportunity to land at another airport, as thick fog enveloped the site.
It is not clear who on the plane gave the ultimate approval for the pilots to attempt a landing.
However, according to subsequent Polish and Russian official reports, the plane flew too low into the treetops of woodland surrounding the airport and crashed.
Poland's current ruling party Law and Justice, chaired by Lech Kaczyński's twin brother Jarosław, won the 25 October general election, and it has started a new probe into the disaster.
However, opposition MPs have accused Defence Minister Antoni Macierewicz of only hiring commission members who will be sympathetic to his theory that the disaster was “an act of terrorism.”
Responding to accusations that the commission is “unrepresentative”, Macierewicz claimed on Wednesday that he is open to broadening the group of investigators. (nh/pk)