A tragic helicopter crash over the Hudson River killed six people—five family members from Spain and their pilot—during a brief sightseeing flight in New York.

Footage captured the helicopter’s main rotor detaching mid-air and spinning away, causing the aircraft to flip and crash into the river. Aviation expert Julian Bray pointed to possible failure of the “Jesus nut,” a vital bolt that secures the rotor system. “If this fails, the helicopter is uncontrollable,” he explained.

The victims were identified as Siemens Spain president Agustín Escobar, his wife, and their three young children. They were on a vacation tour when the Bell 206 helicopter crashed just 18 minutes after takeoff.

Authorities are investigating the cause, but early signs and eyewitness video suggest “catastrophic mechanical failure,” not engine trouble.

Bray emphasized the severity: “The aircraft literally disintegrated in the sky.”