Accident Overview
The airplane broke up in flight and impacted terrain. A search and rescue crew located the airplane after a family concerned alert notification (ALNOT) was issued.
Radar Data
Radar data showed a target consistent with the accident airplane at a mode C reported altitude of 12,300 feet mean sea level (msl) at 1103:45. The target continued westward, and at 1104:56 the mode C altitude was 5,000 feet, corresponding to a calculated 9,400 feet per minute (fpm) rate of descent. The last target appeared 12 seconds later at 1105:08 at a mode C altitude of 3,300 feet.
Wreckage Distribution
The primary wreckage consisted of the fuselage, right wing, landing gear, and engine. The left wing was located one mile west of the main wreckage on the eastern slope of a mountain peak. The left main wing spar separated from the inboard stub section; compression wrinkles were noted in the webbing of the outboard left main wing spar. The lower spar cap exhibited a smooth fracture surface and the upper spar cap an angular fracture surface, features consistent with wing failure under negative aerodynamic loading. The right wing main spar remained attached to the stub carry-through spar, and its webbing was also wrinkled.
Meteorological Conditions
Analysis disclosed that a strong west-southwesterly jet stream was advecting mid- and high-level moisture from off Baja, California, into the southwestern United States. Light rain and rain showers were occurring over southern California associated with this moisture advection. The closest weather reporting facility was somewhat downstream of the accident location relative to cloud movement. Observations from that facility during the hour before the accident indicated the cloud ceiling lowered during that period to about 11,000 feet. One Pilot Report (PIREP) near Blythe, California, confirmed towering cumulus (TCU) in the area. Radar and satellite data indicated convective clouds in the accident area that were rapidly increasing in altitude with very strong vertical motion around the accident time. Deviations in the accident airplane's mode C altitude data just before the accident indicated strong up- and downdrafts were present. Strong jet stream winds near 100 knots were present at the height of the convective clouds. Therefore, isolated strong convective downdrafts were possible in the area of the breakup.
Pilot Actions
While proceeding westbound, the airplane was probably in the vicinity of the northern edge of a rapidly developing convective buildup. The pilot probably encountered moderate to severe turbulence due to strong updrafts and downdrafts just before the accident.