Federal investigators said the pilot had discussed icing with controllers just before the plane went down but were unsure what role, if any, icing played in the crash.
The New York investment banking firm Greenhill & Co. said two of its managing directors, Jeffrey Buckalew, 45, and Rakesh Chawla, 36, as well as Buckalew's wife and two children, were on the plane that crashed on Interstate 287.
Buckalew was the registered owner of the single-engine plane and had a pilot's license.
Wreckage was scattered over at least a half-mile-wide area, with a section found lodged in a tree of a home about a quarter-mile away, near a highway entrance ramp.
Chris Covello of Rockaway Township said he saw the plane spin out of control from the car dealership where he works in Morristown, near the site of the crash.
"It was like the plane was doing tricks or something, twirling and flipping. It started going straight down. I thought any second they were going to pull up. But then the wing came off and they went straight down," he said.
The high-performance, Socata TBM-700 turboprop had departed from nearby Teterboro Airport in New Jersey and crashed about 14 minutes into its flight. It was headed for DeKalb Peachtree Airport near Atlanta.
The pilot had a seven-second call with a controller about icing shortly before the crash, said Robert Gretz, an investigator with the National Transportation Safety Board, told a late-day news conference.
Gretz said he did not know if the pilot was reporting icing had occurred or was questioning the location of possible icing conditions. He said he was unaware of any icing on the ground that would have required deicing.
The Federal Aviation Administration said the pilot had requested clearance to a higher altitude shortly before the plane dropped off radar. The NTSB said the plane had climbed to 17,500 feet.
On an audio recording available online, an air traffic controller is heard telling the pilot about "moderate rime," or a coating of ice particles, up to 17,000 feet.
"We'll let you know what happens when we get in there," the pilot says. "If we can go straight through it, that's no problem for us."
A few minutes later, a different controller is heard telling another pilot about reports of moderate to severe icing up to 14,000 feet and moderate icing up to 17,000. "Pretty much everyone I'm talking to has had at least light to moderate," she says. "I've had one report of extreme at 14."
The crash left charred wreckage across the median and the highway, a heavily used route that wraps around the northern and western edges of the New York City area. A huge ball of charred metal sat in the middle of the northbound lanes. Both sides of the highway were shut down, only partly reopening by late afternoon.
Gretz said the plane just missed a pickup truck on the southbound lanes before crashing into the median, then scattering wreckage across the wooded area and into the northbound lanes.
David Williamson, 19, was doing maintenance at a golf course in Morristown when he spotted a plane in trouble, with smoke coming off both sides of the wings.
"It was really scary," he said.
When the plane crashed, he said, it sent up a "huge plume of thick black smoke."
Gretz said witnesses interviewed by investigators also described the descent as an uncontrolled spin.
Greenhill & Co. said Buckalew's wife, Corinne, and the couple's two children, Jackson and Meriwether, were traveling with him.
"The firm is in deep mourning over the tragic and untimely death of two of its esteemed colleagues and members of Jeff's family," the company said in a written statement.
Authorities said a dog aboard the plane was also killed. The occupants of the plane were headed to Georgia for a combination of personal and business reasons, Gretz said.
Associated Press writers Shawn Marsh and Beth DeFalco in Trenton, and Dave Porter in Newark, contributed to this report.