A private jet with four people onboard crashed Sunday in the Baltic Sea off the Latvian coast.

It was supposed to touch down in Germany but passed its destination while air traffic controllers tried unsuccessfully to contact the occupants, CBS News reported Monday.

German businessman Karl-Peter Griesemann was onboard along with three other people, according to a spokesperson for Quick Air, a charter company in Cologne.

Griesemann was reportedly the pilot and was accompanied by his wife, his daughter, and her boyfriend.

“A Cessna 551 that was flying from Jerez was supposed to land in Cologne but the pilot didn’t answer ATC calls and the aircraft contiued to fly on autopilot in a straight line before it lost altitude and crashed into Baltic sea close to the Latvian coast,” Flightradar24 said in a social media post Sunday.

An image showed the plane’s path over France and Germany and another appeared to show how it had moved in circles over the sea:

Meanwhile, fighter jets from Germany, Denmark, and Sweden were scrambled to attempt contact with the crew during its flight across Europe but saw no one, according to Swedish search and rescue operations head Lars Antonsson.

The Cessna eventually crashed into the sea near a place called Ventspils a few minutes before 8:00 p.m. that evening. It quickly lost altitude and went down after running out of fuel, per Antonsson.

Video footage showed the plane’s flight track as it traveled toward the Baltic Sea where it abruptly stopped:

Latvian, Lithuanian, and Swedish rescue teams working at the crash site reportedly found pieces of the plane.

However, no human remains were found, Antonsson said, adding, “We have no explanation at all, we can only speculate” about what caused the incident “but they were clearly incapacitated on board.”

Meanwhile, aviation safety expert Hans Kjäll told Swedish reporters that issues with the cabin’s pressure may have resulted in those onboard losing consciousness, according to Deutsche Welle (DW).

“If confirmed, this would be the sixth time that a so-called ghost plane — where those on board were incapacitated — has crashed since 1980,” the outlet said.