OKLAHOMA CITY (AP) -- A witness reported seeing a flash in the sky before a medical helicopter crashed into the parking lot of an Oklahoma City nursing home, killing two people, according to a preliminary report released from the National Transportation Safety Board.

The Feb. 22 crash occurred shortly after takeoff and killed pilot Mark Montgomery and flight nurse Chris Denning. Paramedic Billy Wynne was critically injured.

The helicopter operated by Wichita, Kan.-based Eagle Med LLC took off from Integris-Baptist Medical Center about four minutes before the 5:42 p.m. crash. It was headed to Watonga, about 70 miles away, to pick up a patient going to an Oklahoma City hospital.

A man driving in the area told NTSB investigators he saw a "flash" in the sky in front of him and then witnessed the helicopter in rapid fall before it disappeared behind some buildings, according to the report released Wednesday.

"He then drove toward an area where smoke was emanating and saw that the helicopter was on fire in the parking lot of (the nursing home). He immediately assisted others . . . in pulling the surviving paramedic away from the burning aircraft," the report said.

The report did not indicate what may have caused the flash.

Satellite data showed that the helicopter left the hospital and began a gradual climb on a northwesterly path toward Watonga. The data stopped approximately 3 minutes and 30 seconds into the flight, the report said.

An Eagle Med spokesman did not immediately return a phone call seeking comment.

Integris-Baptist spokeswoman Brooke Cayot referred questions to Eagle Med, saying the hospital wouldn't comment until the NTSB released its final report. That could take more than a year.

The Commission on Accreditation of Medical Transport Services has said Eagle Med had just received its three-year accreditation. That included an analysis of maintenance records of all its aircraft and crew.