The estate of late NASCAR legend Greg Biffle is being sued for a total of $30 million following a fatal plane crash that killed seven in December.

Biffle, his wife Cristina, their 14-year-old daughter Emma and 5-year-old son Ryder were killed in the crash, while pilot Dennis Dutton, his son Jack Dutton and Craig Wadsworth also perished.

Now, the estates of the Duttons have filed separate wrongful death lawsuits worth $15 million each, with the suits claiming that the Cessna C550 plane  —  which was owned by Biffle  —  was not maintained properly.

Following the crash, which happened at Statesville Regional Airport in North Carolina, the National Transportation Safety Board (NTSB) said in a preliminary report that Jack Dutton was operating as the co-pilot next to his father.

However, the NTSB said that the younger Dutton was “not qualified” to operate as the second in command.

The initial report relayed that, less than 10 minutes after take-off, Jack said: “…we’re having some issues here.”

Furthermore, the report stated that the left engine had trouble starting at the beginning of the flight.

The death of Biffle and his family on Dec. 18 was confirmed by Rep. Richard Hudson, who said at the time he was “devastated” by the incident.

“They were friends who lived their lives focused on helping others,” Hudson said. “Greg was a great NASCAR champion who thrilled millions of fans. But he was an extraordinary person as well, and will be remembered for his service to others as much as for his fearlessness on the track.”

The NTSB is still investigating the accident.

Biffle, who was 55 at the time of his death, was named one of NASCAR’s 75 greatest drivers, and notched 19 victories during his Cup Series career.

His family’s home was burglarized just weeks after the fatal crash.

The burglary is now being treated as a possible inside job.