GREEN COVE SPRINGS, Fla. -

A helicopter carrying three people to pick up a heart for transplant struck several trees as it crashed to the ground in north Florida, but the pilot made no distress call, according to a preliminary investigation.

The Dec. 26 crash killed a St. Augustine veteran pilot and a heart surgeon and a procurement technician from the Mayo Clinic in Jacksonville. They were flying to a Gainesville hospital to pick up a heart for a transplant in Jacksonville.

According to the preliminary report the National Transportation Safety Board posted late Tuesday, the helicopter took off from the Mayo Clinic at 5:37 a.m.

No flight plan was filed. The last communication from the helicopter came at 5:49 a.m. when the pilot, E. Hoke Smith of SK Jets, contacted the air traffic control tower at Jacksonville International Airport to inquire about the status of restricted airspace. Air traffic controllers told Smith the restricted areas were inactive, and Smith acknowledged their reply, investigators said.

The helicopter, a Bell 206B, was last recorded on radar at 5:53 a.m. at an altitude of 300 feet and about a mile north of the Clay County crash site, investigators said. Its altitude varied from 200-700 feet througout the flight.

The helicopter crashed at 5:54 a.m. in a remote wooded area about 12 miles northeast of the Palatka Municipal Airport in overcast, somewhat misty conditions, according to the report.

Mayo Clinic staff alerted authorities that the team was overdue and a Jacksonville Sheriff's Office aircraft spotted the wreckage about four hours later.

Several trees that were severed by breaks at descending altitudes marked the start of the debris field, investigators said. The first tree strike was at an estimated height of 30 feet above the ground, which severed a roughly 50-foot tree at a ground elevation of 118 feet, according to the report.

"In a very short period of time, he goes from 300 feet to hitting trees. So a lot was going on," said attorney Don Maciejewski, who specializes in aircraft accidents. "I don't think he had visual perspective. I really don't."

The crash ignited a fire that burned about 10 acres of woods and investigators said most of the wreckage was consumed by the fire.

Maciejewski said conclusions can be drawn from the size of the debris field. The NTSB report says the debris stretched 320 feet one way and 70 feet the other way. Maciejewski said that for a helicopter crash, that's a relatively small debris field, and he said his experience tells him that rules out mechanical error.

"I think he clipped a tree. That's my opinion at this point," Maciejewski said. "He clipped a rather high, large tree, and after that, if you knock your rooter system out of balance, you're just along for the ride."

"The whole picture of the crash site, if you've done a lot of these cases, shows that this was a controlled flight into terrain," Maciejewski added. "That sounds funny, but it means the pilot thought he was here when he wasn't here, and he flew it into the ground. ... That's what 35 years of flying and doing air crash cases tells me."

The NTSB investigation into what caused the crash may take up to a year and a half to complete.

The crash killed Smith, 68, a Vietnam combat veteran, and two Mayo Clinic staff: surgeon Luis Bonilla, 49, and technician David Hines, 57. Bonilla had transferred in November to the Jacksonville hospital from the Mayo Clinic in Rochester, Minn.

The patient who had been waiting for the heart was put back on the transplant waiting list.

Messages left Wednesday for Smith's son, who is the general manager of SK Jets, and a Mayo Clinic spokesman were not immediately returned.

To read the full preliminary crash report, click here.