MANCHESTER, Ky. (AP) — The crash of a medical helicopter that killed three crewmembers in southeastern Kentucky on Thursday was the fourth deadly accident in the past six years for Air Evac Lifeteam, a Missouri-based company that operates from 114 locations in 15 states.

The helicopter that crashed Thursday night in Clay County had been completely refurbished just over a year ago making it "more powerful and capable of carrying higher gross weight," company spokeswoman Julie Heavrin said.

"We are devastated at this loss," company president Seth Myers said in a statement. "These were members of our family. Our focus at this time is on providing support for the family and friends of these crewmembers."

There was no patient on board. The helicopter, a Bell 206 LongRanger, came down in the parking lot of Paces Creek Elementary School outside Manchester, which is about 90 miles southeast of Lexington. Witnesses described a light fog, though forecasters said there was no severe weather in the area.

The last fatal Air Evac Lifeteam crash was in Arkansas in 2010. All three crew members were killed when that helicopter, a Bell 206 built in 1978, went down in Van Buren County. Heavrin said Air Evac Lifeteam has had two other fatal crashes in recent years. One in Indiana in 2008 killed all three crew members, as did the other in Alabama in 2007.

There have been 32 crashes in the U.S. involving Bell 206 helicopters since June 2011, with a total of 12 fatalities occurring in seven of the crashes, according to data from the National Transportation Safety Board. The most recent crash recorded was May 10 in Hartford, Ky. The pilot was not injured after the craft struck a power line.

The company identified the crewmembers as pilot Eddie Sizemore, flight paramedic Herman "Lee" Dobbs and flight nurse Jesse Jones. They were on their way back to base in Manchester after transporting a patient to a hospital in London, Ky.

Suddenly, "You just started hearing this 'WHA-WHA-WHA,' and then it sounded like four, big 'bang-bang-bang-bang,' like that," Kelly Bailey, who lives near the school, told The Lexington Herald-Leader. "And then you heard this big, huge boom."

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Her husband Kenneth said the couple saw flames after the crash.

"We get to the window and see this huge fireball," he said. "It was just a huge fireball over there."

Laurel County Sheriff's spokesman Gilbert Acciardo told the Herald-Leader that Sizemore had retired as a deputy from the sheriff's office, but returned in 2011 before leaving the position to become a pilot for Air Evac Lifeteam.

"He enjoyed flying," Acciardo said. "That was his passion."

Air Evac Lifeteam President and CEO Seth Myers said the company is devastated by the loss of the crew.

An investigator with NTSB arrived on Friday to investigate and the crash scene will likely be cleared over the weekend, NTSB spokesman Peter Knudson said. The investigator will compile a preliminary report of the crash within about two weeks, Knudson said.

The Missouri-based company has been providing medical transportation for 26 years. Its flight crews typically consist of a pilot, registered nurse and paramedic. Besides its fleet of helicopters, Air Evac Lifeteam also uses planes, including one based at the nearby Williamsburg-Whitley County Airport in southeastern Kentucky.

Judy Owens, former head of the University of Kentucky Center for Rural Heath in Hazard, said the mountainous terrain of central Appalachia makes helicopter transport a must if patients are to arrive at major hospitals within the so-called "golden hour" that can determine whether they live or die. Owens said the flight crews are considered heroes in central Appalachia.

Blair Marie Beggan, a spokeswoman for the Association of Air Medical Services, said the United States now has about 850 medical helicopters in service full-time and that they transport about 400,000 critically ill and injured patients each year.