Dr. Richard Rockefeller, son of the billionaire and prominent philanthropist David Rockefeller, was killed Friday morning when the small plane he was piloting crashed shortly after takeoff, according to a spokesman for the family.

Dr. Rockefeller, 65, was the only person on board the plane, which the authorities identified as a Piper Meridian single-engine turboprop.

The cause of the crash was not immediately clear.

Dr. Rockefeller took off from Westchester County Airport at 8:08 a.m., departing from Runway 16 into dense fog and steady rain. Less than 10 minutes later, the Federal Aviation Administration notified airport officials that it could not reach the pilot.

At 8:23 a.m., the local police reported that the plane had crashed less than a mile from the airport, near Cottage Avenue in the town of Harrison.