The helicopter that crashed Thursday in a field in Lino Lakes, killing two people, was in flight earlier that day with no known mechanical problems, authorities said Friday.

The chopper came down in a field off Main Street and Sunset Avenue, near a cluster of homes, about 5:30 p.m. Thursday, according to Anoka County Sheriff's Cmdr. Paul Sommer.

Witnesses said they saw the helicopter, which was flying northeast, experience sudden distress. They heard a pop, saw the rotary blade stop turning, and then saw the helicopter drop from the sky.

"There was no possibility that any occupants of the aircraft could have survived," Sommer wrote in a statement Friday morning.

The helicopter was a 1982 Fairchild Hiller FH-1100, a model originally built for the U.S. Army as a light observation aircraft. It was in flight previously Thursday and originated from the Anoka County Airport in Blaine, Sommer said.

The victims are believed to be a 48-year-old man from Minneapolis and a 47-year-old woman from Blaine. Their names are being withheld pending notification of family and official identification of the remains.

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A helicopter crashed in a field near Sunset and Main Street in Lino Lakes.

However, a Louisiana-based pilot who requested anonymity Friday, citing respect for the official identification process, described the man as his longtime friend and a veteran commercial airline pilot. The woman who was killed was his girlfriend, the pilot said.

The Louisiana pilot previously ran a helicopter training company and said he worked with the victim in that same helicopter last fall. "He was a great pilot, he was very knowledgeable and methodical," he said.

The chopper is registered to Helicopter Connection LLC, which lists its address at a post office box in south Minneapolis.

Joe Harris, manager of the Anoka County Airport, confirmed that it had departed the airport at least one other time Thursday before the fatal second trip. It remains unclear if the helicopter is one of eight the airport permanently houses for private operators.

The Federal Aviation Administration and the National Transportation Safety Board are investigating. It isn't the first encounter they've had with the helicopter that crashed. In 2006, while registered to Helicopters of Northwest Florida in Navarre, Fla., the pilot heard a "bang" and a shudder. It was discovered that the tail rotor had separated from the craft at 600 feet, according to the NTSB accident report. The pilot in that case was unharmed. And back in 1985, the copter was damaged and then wasn't operated for the next 18 years, according to flight records.

Gary Robb, an attorney based in Kansas City, Mo., who specializes in helicopter crashes, dubbed the accident a "real human tragedy" Friday. Based on witness statements, Robb said he believes the crash was probably caused by an in-flight mechanical malfunction — a scenario with a much lower survival rate than in a fixed-wing aircraft.

"That's the danger of a helicopter — you can't glide it," Robb said. "If you don't have control over the main rotor blade, it drops like a rock. Even the best pilot is helpless."

Authorities asked residents to call Lino Lakes police at 763-427-1212 if they find any unusual objects in their yards that might be debris from the helicopter. Do not pick up or move the objects, they cautioned.

It was the second helicopter crash in the region in three weeks. Last month, three emergency workers were seriously injured when a North Memorial Medical Center helicopter went down on the east side of Lake Winona en route to the airport in Alexandria, Minn. That incident remains under investigation.

Liz Sawyer • 612-673-4648