TAMPA, Fla. (WFLA) — Divers were in the Hudson River Friday continuing to search for evidence in Thursday’s tourist helicopter crash.

Six people died, including three children. The family was visiting the U.S. on vacation from Spain. The helicopter broke apart midair and plummeted into the water.

It’s a mystery how this a happened, and officials with the National Transportation Safety Board (NTSB) said Friday was the first full day of the investigation.

“We have a lot of information but we do not speculate,” said NTSB Chairman Jennifer Homendy.

News Channel 8’s helicopter pilot Roy Harkness pointed out the missing pieces of the helicopter from the stations new bird.

“We know for sure that the entire rotor system came off the aircraft as a unity, and fell as a unit,” Harkness said. “Horrific is the first word to come to mind. Then, for all practical purposes, unsurvivable.”

Harkness said he saw videos of the crash and noticed how the first thing to break was the tail boom. But the videos don’t show how or why, which he hopes to get clarity on soon.

“As a pilot I want to know why so I can make sure it doesn’t happen to our bird… It’s the same make and model,” Harkness said.

News Channel 8 On Your Side took a quick flight above downtown Tampa. Lift off was easy and Harkness said when we take care of these helicopters, they take care of us.

“These aircraft are really, really safe. When they’re maintained properly and flown properly, they are one of the safest aircraft in the sky,” Harkness said.

John Cox is an aviation expert who said there will be a preliminary report by the NTSB in 30 days, and then determining a probable cause could take between 12 to 18 months.

“There have been similar events — not very many — but there have been cases where this type of breakup, and it’s usually been in turbulence or what they call a low G condition, and that’s when the main rotor blades contact the kill boom and the loss of the tail boom results in the loss of control of the helicopter,” Cox said. “Then, at that point, the main rudder system departs the helicopter. So there is some indication of history, and the NTSB will look at that very closely.”