Indonesia's air force chief said that an investigation into the cause of last week's crash of a military transport plane in Medan, that killed about 130 people, did not need the assistance of experts from the plane's United States manufacturer.

"We have experts. We don't need any third-party involvement," Air Force Chief Marshal Agus Supriatna told reporters last night during a doorstop.

He did not say when a full report of the crash investigation would be released to the public.

Chief Marshal Agus said preliminary investigations suggested one of the plane's four engines stalled after take-off.

He said a ground antenna located near the airport contributed to the accident.

"When an engine stalls, a pilot would reduce speed and, as a result, the plane would descend, and it was then that the plane hit a ground antenna tower.

"The plane then turned to the right and crashed into shophouses. We will make further analysis from here," he said.

The Lockheed C-130 Hercules is a four-engine turboprop transport aircraft that Indonesia bought from the US in 1964.

Indonesia has been using Hercules planes to transport logistics supplies and soldiers and their family members.

An air force officer told The Straits Times that the 35m antenna tower, most of which was knocked down by the Hercules, is owned by a private school.

He added that the tower was built without a permit.

The transport plane crashed within an area near the airport that is strictly regulated.

"The height of any building in such areas is regulated and an antenna that high shouldn't be there," said the officer, who spoke on condition of anonymity.

Chief Marshal Agus also denied the plane was overloaded.

A total of 122 people were on board the plane.

They were mostly servicemen and their families.

Relatives of some civilians from non-military families said they paid between 700,000 rupiah and one million rupiah (S$70 and S$100) to travel on the aircraft.

The military has denied taking payments and has vowed to investigate their claims.