(Adds comments from NTSB official, previous OLYMPIA, Wash.)
By Jonathan Kaminsky
FEDERAL WAY, Wash., March 19 (Reuters) - Investigators combing through the wreckage of a news helicopter that crashed near the Seattle Space Needle were looking into reports of a strange noise before the accident but have yet to pinpoint a cause of the crash, an official said on Wednesday.
The chopper fell to the street and burst into flames on Tuesday in a popular downtown tourist area after an attempt to take off from a helipad atop a television news station. The pilot and a photographer on board were killed.
Three vehicles on the street caught fire but their occupants escaped alive, although one was severely burned.
Investigators have moved the wreckage of the chopper to a hangar at an airport in the Seattle suburb of Auburn.
They plan to extract the engine and examine it before shipping that part to Texas, where the engine manufacturer is based, said Dennis Hogenson, a deputy regional chief for the National Transportation Safety Board.
The NTSB has said witnesses reported an unusual noise from the aircraft during its departure, but Hogenson said some of them may have been unfamiliar with the normal sound of a helicopter.
"We're going to try to understand exactly where that noise was originating from and what caused it," Hogenson told a news conference in the city of Federal Way.
"And we don't know yet if it was an airframe noise, an engine noise. It may have been a noise from something external to the helicopter, we just don't know yet," he said.
Investigators were also looking into radio communications between the pilot and crane operators near the helipad, although Hogenson said there was no substantial evidence to indicate a connection between cranes and the crash.
Officials from Airbus Helicopters, the maker of the 11-year-old Eurocopter AS350, and the engine's manufacturer, SAFRAN Turbomeca USA, are involved in the probe, said Hogenson, whose agency plans to release a preliminary report by Monday.
Seattle plans to review its rules for helipads in the aftermath of the crash, mayor's spokeswoman Rosalind Brazel said. City officials said medical facilities and news organizations are allowed to operate helipads.
In January, the NTSB said helicopter operations were among its priorities for improving transportation safety. It said over 500 deaths since 2004 in accidents involving choppers for search and rescue missions, medical transport and commercial operations was "unacceptably high."
Harborview Medical Center spokeswoman Susan Gregg said that Richard Newman, 38, a motorist who suffered burns over 20 percent of his body, was improving and had resumed breathing on his own. She said he would need surgery.
The pilot Gary Pfitzner, 59, had worked for Illinois-based Helicopters Inc, which operated the chopper for KOMO television station. Photographer Bill Strothman, 62, who shot video for KOMO, had retired from the company and worked as a freelancer, according to the station.
The Space Needle and Seattle Monorail, which had been closed after the crash, resumed normal operations on Wednesday, the mayor's office said. (Writing by Alex Dobuzinskis; Editing by Cynthia Johnston)