A pilot operating the world’s only 1944 Northrop N9M Flying Wing plane is reportedly deceased after the aircraft crashed on the grounds of a prison in Norco, Calif. Details on the incident are still vague; it seems no bystanders were injured but the plane appears to have essentially disintegrated on impact.

A witness described the plane as “dipping” left and right before the fatal crash at the grounds of the California Rehabilitation Center just after noon Monday, in an interview to . The news outlet reports that the plane was maintained by the Planes Of Fame air museum in Chino, nearby, which is hosting an air show early in May.

As of this writing, the NTSB and FAA are both investigating but neither the pilot’s name nor the cause of the crash have been released.

As for the unusual-looking N9M plane, has on its website that it was “the fourth and final in a series of [one-third] scale test models for the Northrop XB-35 flying Wing bombers.” It’s also described as “the grandfather of today’s .”

The air museum got this N9M in particular in the 1950s, started restoring it in 1981 and started flight testing in 1996. It was a relatively compact 17 feet, 10 inches long with a 60-foot wingspan.

Planes Of Fame’s N9M was the last operational aircraft of its type, though obviously the loss of the pilot is infinitely more tragic.