The plane crashed into the rugged mountainside near the Apex ski resort, west of Penticton. (CBC)

A plane that crashed into a heavily forested mountainside in B.C.'s southern Interior last week, killing the four men aboard, may have nosedived into the ground, say officials.

The wreckage of the Piper Comanche PA24 was found after an eight-day search Wednesday near the Apex Mountain ski resort, about 25 kilometres west of Penticton.

Transportation Safety Board inspector Bill Yearwood says initial information points to a rapid descent into thick bush.

"Given the way the aircraft disappeared into the terrain, it's consistent with a steep descent. And when the aircraft is descending in a very steep descent, that's normally because the pilot lost control for some reason or another," said Yearwood.

TSB Investigators expect to arrive at the wreckage site Thursday morning to begin their investigation, he said.

"We look at the operation. We look at the environment, the aircraft, the mechanics of it and, of course, the human element of it — whether there were any human factors that could have contributed to the crash."

The Piper Comanche PA24 was similar to this one. (Adam Hunt)

Yearwood noted the weather was calm and hot on the day of the crash, and such conditions can make a plane's takeoff and initial climb more difficult.

The names of the four dead men have not been officially released, but the pilot was Rama Tello from Kelowna. The passengers were his brother and two other men who were on board for the short trip from Penticton to Victoria.

Military and civilian personnel spent eight days searching for the plane, before a search-and-rescue spotter noticed a glint of metal in the trees.

A friend of the missing men offered a $10,000 reward, which prompted several people to search with their private aircraft, nearly causing a second crash when one of the private planes nearly hit a search aircraft.