Investigators have found part of the tail of the jet that crashed in South Florida over the weekend more than a kilometre from the crater caused when the aircraft made impact.

National Transportation Safety Board member Tom Chapman said during a news conference Tuesday that the discovery of tail parts broken into three pieces confirms the plane was breaking apart before it hit the ground.

Three pieces of the tail's elevator were found over a range of about two to six kilometres from the crater site.

"It seems implausible that it would have been a result of the impact," he said. "It would have separated before the impact." Without the tail intact, the plane wouldn't have been able to pull up from its nosedive, he said. But Chapman added he's not sure it would have been effective even if it was intact because of the extreme speed of the aircraft's descent.

"The function of the elevator is to control the pitch up and down," he said. "At those speeds I don't know that it would've been effective even if it had still been attached to the aircraft, but knowing that it was lost is a very important piece of evidence in terms of pointing us towards other things to investigate." Florida crash: How did this private jet fall out of the sky? | About That The co-pilot, Nathalia Gadelha Filgueiras, told air traffic controllers minutes before the crash that ice was accumulating on the plane and that severe turbulence had thrown it up and down by more than 210 metres.

Bahamas-bound Learjet 60 hit bad weather Sunday and slammed into the ground about 11 kilometres southwest of Palm Beach. The plane hit the ground with enough force to create a crater before bursting into flames. The impact scattered plane fragments over a large area.

Chapman said significant progress has been made in terms of being able to get access to the crater, where he said investigators expect to find "critical airplane components."

"With the force of that impact, even the elements of the aircraft that are in the crater are going to be very likely in smaller pieces," he said. "So we don't know exactly what all we have yet, but that's part of the investigation.... It's a big puzzle to try to put together." The plane took off from Austin, Texas. The victims included technology entrepreneur Adam Robinson, his wife, Helen Sharp, and their two young children, relatives said. The family's nanny was also with them.

Co-pilot texted before crash Filgueiras' stepfather, Thiago Corteleti, told the New York Post that she texted her boyfriend about 10 minutes before the crash, telling him, "I've got turbulence, I've got ice." The texts were reportedly sent before the situation became critical. In the last two minutes of the flight, Filgueiras shifted from calmly communicating with air traffic controllers to calling out terrifying updates as the plane plummeted.

Audio reveals pilot's frantic call before Florida jet crash November 2 Duration The Federal Aviation Administration prohibits commercial airline pilots from using cellphones at any point during a flight. The rules aren't as strict for pilots of charter flights; they are not supposed to use cellphones during critical phases of flight, such as takeoffs and landings, but are allowed while cruising at altitude unless their company or pilot in command specifically bans it.

Chapman said Monday that weather would be a key focus of the investigation. A preliminary report describing what happened will be released in about a month, but it will likely take more than a year to determine the cause of the crash.