Non-crew members were in the cockpit of a plane that crashed killing the Polish president and more than 90 others, an investigation has found.
The question of whether the crew were pressured to land remains unanswered, an official said.
One of those in the cockpit has been identified, but the BBC has learned it was not the president.
The plane crashed as it tried to land at Smolensk in western Russia on 10 April, killing dozens of senior Poles.
The investigation, which was releasing its preliminary findings of the investigation, confirmed crew were repeatedly warned about poor weather.
Alexei Morozov, head of the technical commission examining the crash, said air traffic controllers had warned twice that visibility was 400m (1,312ft) and that "there were no conditions for landing".
'No regular training'
Then, four minutes before the crash, another Polish plane that had landed earlier that morning said visibility had dropped to 200m, he said.
Mr Morozov also said the crew of eight on board the plane that crashed had been formed several days before the flight and "did not undergo regular simulated training, including the practice of co-ordination and emergency situations during flights".
The Tupolev-154 presidential plane was in full working order when it crashed, Mr Morozov said, according to a report by Russian news agency Itar-Tass.
He said systems at the Smolensk airport where the plane was trying to land were also operating normally.
The investigation, which was carried out by the inter-state air committee for the former Soviet Union, ruled out any terrorist attack, explosion, or fire on board the aircraft.
The plane was flying President Lech Kaczynski and the other passengers to an event commemorating the 1940 Katyn massacre of more than 20,000 Poles by Soviet forces.
Shortly after the crash, there was speculation that passengers may have put pressure on the crew to land in Smolensk, though Polish officials said at the time that there was no evidence to substantiate such claims.
On Wednesday, the head of the inter-state air committee, Tatyana Anodina, said that possibility should be investigated, and that the issue was of "vital importance for the investigation of the causes [of the crash]".
'Cabin door open'
She said the investigation had established "in the cockpit there were individuals who were not members of the crew".
"The voice of one of them has been identified exactly, the voice of the other, or the others, will require additional information from the Polish side," she said.
The investigation found that the pilot's cabin door was open as the plane tried to land and the voices of the crew were hard to identify, Itar-Tass reported.
Ms Anodina stressed that the crew had received "timely information about weather conditions and alternate airfields", and that there had been no equipment failure.
"The engines were working up till the moment the plane collided with the ground," she said.
She added that she was confident that investigators would establish the causes of the crash as quickly as possible.
Results would be made available to authorities in Russia and Poland, and to the public, she said.