The defendants are accused of downing Flight PS752, killing all 176 passengers and crew on board. Over 103 relatives of the victims and their lawyers attended the court hearing in Tehran on Sunday.
Meanwhile, the judge in charge of the case said all those who lost their loved ones may attend the proceedings. He also vowed that the trial will be fair and anybody responsible for the incident will be punished.
Iranian military officials say the defendants shot down the aircraft unintentionally as they took it for an enemy projectile or plane.
The incident happened as Iranian air defense systems anticipated an enemy attack because shortly before that, Iran had battered a US base in Iraq in retaliation for the assassination of top Iranian General Qassem Soleimani.