A plane crash that killed three family members near Glencoe, Minn., earlier this year resulted from the 52-year-old pilot flying into conditions for which he wasn't equipped or trained, causing him to lose control and the plane to break apart in midair, federal investigators have determined.

Pilot Stuart Dahlberg of Brooklyn Center, who was not certified to fly by instruments, flew into low clouds not long before his single-engine plane crashed into a muddy farm field about 11:12 a.m. on March 21, about 4 miles north of Glencoe, according to a report on the crash issued this month by the National Transportation Safety Board (NTSB).

The fiery crash, about 54 miles west of Minneapolis, killed Dahlberg, his wife, Ivelisse Morillo Dahlberg, 36, his 76-year-old mother, Mae Dahlberg of St. Cloud, and three pet dogs. They were flying from Crystal Airport to Craig, Colo., to watch a high school play directed by Stuart Dahlberg's sister.

Dahlberg's brother David, who immediately after the crash had praised Stuart Dahlberg's care and caution as a pilot, couldn't be reached Wednesday.

The crash of the 1947 single-engine Beechcraft Bonanza, which Stuart Dahlberg owned, left a 900-foot-long swath of torn and burned debris across two plowed fields, the NTSB report said.

The debris included pieces of wing, fuselage and control cables, all torn and broken in ways consistent with "overstress failure" and "tension overload," the report said.

Many crashes have resulted from pilots getting "spatial disorientation" in bad weather and putting too great a strain on the aircraft while trying to control it, according to the Air Safety Institute, a division of the Aircraft Owners and Pilots Association.

Pilots stuck in such situations "often fall prey to the so-called 'graveyard spiral,' -- a descending turn that only gets tighter and steeper as the pilot pulls back on the yoke in a misguided attempt to stop the descent," according to a bulletin for pilots published by the institute.

"Unusual attitudes can put tremendous strain on an airframe, and a panicked pilot lost in the soup can push an aircraft literally to the breaking point," the bulletin said, adding that low clouds should be studiously avoided by pilots who aren't equipped and rated to fly by instruments.

"Thunderstorms, icing, high winds, turbulence -- none of these more dramatic, high-profile threats comes close to killing as many pilots as simple, condensed water vapor," the institute's bulletin concludes.

Neither Dahlberg's pilot's license nor the logbooks provided by his family members reflected that he'd had any training to fly by instruments, the NTSB report said. In addition, the plane, while certified air worthy for normal operations, did not have the instruments necessary to fly without normal visibility, the report said.

However, weather observations at the Glencoe Municipal Airport, about 5 miles south of the crash site, indicated that it was overcast and misting, with a cloud ceiling of 900 feet, around the time of the crash, the NTSB report said.

The report also included indications that Dahlberg was less than fully prepared for the flight:

"The pilot did not request weather information for his route of flight, nor did he file a flight plan."

Larry Oakes • 612-673-1751