National Transportation Safety Board examiners were collecting the helicopter's wreckage on Wednesday before transporting it to Nashville for reconstruction and further examination.
Two Le Bonheur Children's Hospital workers and the pilot died when the helicopter rammed into the ground and caught fire while on the way to pick up an ailing child in Bolivar (BAW'-luh-vuhr). The helicopter crashed in Somerville, about 45 miles east of Memphis.
Data from a ground-based satellite tracking service shows the helicopter was traveling eastbound at about 1,000 feet before turning south in the moments before going down, NTSB investigator Ralph Hicks said. There's no indication the pilot of the three-bladed Eurocopter transmitted he had a problem before the aircraft crashed.
The aircraft's wreckage and maintenance records, plus weather information and witness statements, will be examined during the investigation, Hicks said.
A preliminary report is expected in about seven to 10 days. A final report could take nine months to a year or more, NTSB officials said.
"It's going to take quite a while to get to the bottom of everything," Hicks said.
The sick child was not aboard the aircraft when it crashed and was eventually taken by ground ambulance to Le Bonheur.
The helicopter was operated by Hospital Wing, which uses seven helicopters to take patients to hospitals within a 150-mile radius of Memphis. Hospital Wing spokeswoman Lisa Harlow said flights have been suspended.
As a result, Le Bonheur is using the air services of county emergency management departments and other air ambulance providers to bring children to the hospital by helicopter if needed, said Dr. Barry Gilmore, the hospital's chief of emergency services.
Meri Armour, president and CEO of Le Bonheur, said the Hospital Wing helicopter was cleared for both weather and flight plans when it took off. Authorities began searching when the helicopter didn't respond during a routine 10-minute check-in.
Corey Chaskelson, a forecaster with the National Weather Service in Memphis, said there were clouds at about 4,000 to 5,000 feet, but forecasters don't know if weather was a factor.
In a news release, the hospital identified those killed as 47-year-old pilot Charles Smith, 43-year-old nurse Carrie Barlow and 43-year-old respiratory therapist Denise Adams.
Another Hospital Wing helicopter crashed in West Tennessee in March 2010, when the pilot tried to outrun a storm. That crash killed the pilot and two nurses.
At that time, improving the safety of emergency medical services flights was on the NTSB's "most wanted improvements" list.
It first made the list in 2008, a year when the industry suffered a record 28 fatalities in seven helicopter accidents. The agency's focus on the problem may have had some impact.
According to statistics provided by NTSB, 2011 and 2012 each saw only one fatal helicopter emergency medical services crash. But those numbers began to creep up again this year. Including Tuesday's accident, 2013 has seen five fatal helicopter EMS crashes with 12 killed.