AURORA - An investigation into a medical helicopter crash that killed a desperately ill 1-year-old girl and three crew members will include whether a radio tower's lights were on when the aircraft clipped the structure's wire and went down in a suburban Chicago field, authorities said. | NEW video

Investigators also have pieces of the helicopter, including a mangled yellow-and-white rotor, to determine what happened to the Air Angels helicopter that crashed minutes before midnight Wednesday.

The crash caused so much damage to the 734-foor tower that Aurora police advised about 1,000 people who live nearby to leave their homes until engineers believe it is safe.

The helicopter was flying about 50 feet lower than the top of the tower when it hit the wire, said National Transportation Safety Board investigator John Brannen.

"I can say that when I was out here last night after the accident that the lights on the tower were not lit," Brannen said Thursday. The NTSB was investigating whether the lights could have been knocked out during the incident, he said.

The Air Angels helicopter was carrying Kirstin Blockinger to Children's Memorial Hospital in Chicago when it crashed.

Nearly a dozen members of the girl's family visited the site of the crash late Thursday afternoon, filing through tall grass to see the wreckage, one clutching a brown teddy bear and pink roses.

"We love Kirstin and celebrate her life, however short," said her grandfather Steve Ogletree.

Eva Blockinger told The Associated Press that her great-granddaughter often was ill and suffered from seizures.

"She was in and out of the hospital a lot," said Blockinger, 89, of Leland. "It was a regular occurrence."

A snapped wire hung from the tower across a busy road from where the twisted rotor blade could be seen near the field's edge. The crash site farther back was secured by yellow police tape and not visible from the road.

Aurora police Sgt. Chris Whitfield said that after engineers assessed the tower, residents within 1,000 feet of it were advised to evacuate their homes. Police said engineers will use a helicopter to make repairs starting Friday.

Air Angels CEO Jim Adams said operations at the Bolingbrook-based emergency medical transport service were being suspended until company officials can determine with federal investigators that the crash was not an event that could be repeated. Adams said he did not know how long that might take.

The crew members killed were pilot Del Waugh, 69, of Carmel, Ind.; paramedic Ronald Battiato, 41, of Peotone, Ill.; and nurse William Mann, 31, of Chicago. Waugh, a Vietnam vet who worked for Air Angels since 2006, had at least 4,000 hours of helicopter flying experience, said Michael Dermont, the company's director of business development.

Kirstin had been in the emergency room at Valley West Hospital in Sandwich on Wednesday night before it was decided she would be taken to the pediatric critical care unit at Children's Memorial Hospital.

Thursday's accident was the 11th crash this year, and the sixth fatal one involving medical helicopters nationwide, according to NTSB data.

The NTSB plans to hold a public hearing on medical helicopter crashes sometime next year to look into the recent increases in accident rates, said NTSB spokesman Terry Williams.

The Aurora crash was the second involving Air Angels helicopters since its inception in 1998. A January 2003 crash that killed a pilot was later determined to be caused by pilot error and weather. Mechanical problems were blamed for an August 2007 forced landing in which there were no injuries.

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Fatal crashes involving medical helicopters

Here's a look at other recent fatal accidents involving medical helicopters:

• Sept. 28, 2008: A medical helicopter carrying victims of a traffic accident went down in a suburban Washington, D.C., park, killing four of the five people on board. The pilot, a paramedic, a county emergency medical technician and one of the traffic accident victims died. An 18-year-old woman was also injured.

• June 29, 2008: A fiery collision killed six people aboard two medical helicopters arriving with patients at Flagstaff Medical Center in Arizona. Three people died on each of the two Bell 407 helicopters: the pilot, the patient and a flight nurse on one chopper, the pilot, the patient and a paramedic on the other. A flight nurse on one of the helicopters was hospitalized in critical condition and later died of his injuries.

• June 8, 2008: A medical helicopter agreed to pick up a patient in Huntsville, Texas, in the early morning darkness after a Life Flight crew abandoned the mission. The Bell 407 helicopter crashed in Sam Houston National Forest, killing the patient, pilot, paramedic and nurse.

• May 10, 2008: A University of Wisconsin Hospital Med Flight helicopter dropped off a patient in La Crosse, Wis., and then crashed shortly after it took off on its return flight to Madison, killing the surgeon, nurse and pilot on board. The aircraft was a new American Eurocopter EC13 leased from Denver-based Air Methods.

• Feb. 5, 2008: A medical helicopter crashed during a trip to South Padre Island, Texas, to pick up a patient. The helicopter had just aborted its trip due to bad weather when it went down, so there was no patient aboard. The pilot and two medics were killed in the accident.

• Dec. 10, 2006: A medical helicopter crashed northeast of Los Angeles, killing the pilot and two crew members. No patients were on board. The chopper was en route to its base in Victorville, Calif., from Loma Linda Medical Center. A combination of pilot error and weather conditions were to blame, according to the NTSB.

• May 30, 2006: A medical helicopter in Washington, D.C., crashed after aborting a landing at a hospital, killing the patient and injuring three crew members. The patient had been critically ill and was being transported to Washington Hospital Center from Greater Southeast Community Hospital about 10 miles away. The chopper crashed less than a mile from the hospital on a golf course at the U.S. Armed Forces Retirement Home, where the pilot tried an emergency landing. Pilot error caused the accident, the NTSB said.

• April 13, 2006: A medical helicopter on a test flight in Green Bay, Wis., experienced mechanical problems and crashed, killing the pilot. A combination of pilot and mechanical error caused the accident, according to the NTSB.

Sources: The Associated Press and National Transportation Safety Board.