Kieran Daly of Air Transport Intelligence told Al Jazeera the crash had "a devastating impact to the ground, which suggests that either the aircraft was completely out of control and unflyable ... or that for some reason the pilot flew inadvertently into the ground".
Al Jazeera's Alireza Ronaghi, reporting from the crash site near Qazvin, said recovery work will continue through the night.
"Rescue workers [are using] hydraulic shovels and bulldozers, trying to sift through whatever remains in the crater - about four to five metres deep and 10 to 15 metres long," he said.
"Various parts of the aircraft body are shattered around the [surrounding] field ... the wind here is a blessing because it scatters the strong smell of burnt plastic, burnt fuel and burnt flesh - it is so unbelievably overwhelming."
Reports of fire
Witnesses said the plane exploded after it dropped out of the sky.
One witness told Al Jazeera that he saw "something like a huge cigarette, at the end of which it was burning".
He said parts of the flaming plane fell to the ground, setting off blazes wherever they landed.
The plane first dipped low towards houses in the nearby village of Janat Abad, before temporarily regaining altitude, and then crashing to the ground, witnesses said.
The Armenian authorities have said they believe the crash was caused by an engine fire, adding that they are working closely with Iran.
Iranian officials said that recovering the "black box" flight recorder would be crucial in helping to identify the cause of the crash.
"It may be the case that the pilot had said there was an existing fault with the aircraft ... which will point investigators to the cause," Daly said.
The aviation official said Caspian Airlines had a safety record of "varying quality".
"It has a good statistical record but because it has been around for such a short time and is so small, [that] doesn't say very much," he said.
Mahmoud Ahmadinejad, Iran's president, has ordered the transport ministry to launch an inquiry into the accident.
Caspian Airways flight 7908 went down 16 minutes after take-off from Tehran's Imam Khomeini international airport - at 11:33am (07:03 GMT), according to aviation authorities.
Crying relatives and friends of those who died on board the flight gathered at Yerevan airport after hearing the news on Wednesday, where a notice on a wall listed people who were on the flight. Some of those gathered had to be treated for shock by medical personnel.
The crash is one of Iran's worst aviation disasters.
In December 2005, 108 people were killed when a Lockheed C-130 transport plane crashed into the base of a high-rise housing block outside the Iranian capital.
Twenty-nine people were killed in September 2006 when an aircraft came off the runway after landing in the eastern city of Mashhad and burst into flames.
In November that year, a military plane crashed on takeoff at Tehran's Mehrabad airport, killing all 39 people on board.