The board that investigated the loss of the remotely operated Helios Prototype aircraft during a test flight last summer has released its final report. The board determined that the mishap resulted from the inability to predict, using available analysis methods, the aircraft's increased sensitivity to atmospheric disturbances such as turbulence, following vehicle configuration changes required for the long-duration flight demonstration.

Further information on the Helios mishap and its causes is available at on-line at: /centers/dfrc/Newsroom/NewsReleases/2004/04-42.html or the Helios Mishap Investigation Board Report at: http://www.nasa.gov/pdf/64317main_helios.pdf.

Close-up of Helios Prototype solar-electric flying wing during climb on its last flight. Photo number ED03-0180-1 This close-up telephoto from a chase aircraft of the Helios Prototype solar-electric aircraft while climbing on its last flight on June 26, 2003 shows essentially normal dihedral (upward bending) of the long proof-of-concept flying wing prior to its entering turbulent air.

Helios Prototype at high wing dihedral prior to structural failure and in-flight breakup. Photo number ED03-0180-2 This view of the Helios Prototype from a chase helicopter shows abnormally high wing dihedral of more than 30 feet from wingtip to the center of the aircraft that resulted after the Helios entered moderate air turbulence on its last test flight. The extreme dihedral caused aerodynamic instability that led to an uncontrollable series of pitch oscillations and overspeed conditions, resulting in structural failures and partial breakup of the aircraft.

Helios Prototype falling toward the Pacific Ocean after in-flight breakup during last test flight. Photo number ED03-0180-3 Seconds after uncontrollable pitch oscillations and overspeed conditions led to multiple structural failures, the Helios Prototype solar-electric aircraft is shown falling toward the Pacific Ocean, trailed by lightweight debris streaming from the shattered aircraft. A small parachute deployed behind the left wing is part of the aircraft's emergency flight termination system.

Wreckage of the Helios Prototype floats in the ocean after in-flight breakup on test mission. Photo number ED03-0180-4 Wreckage of the Helios Prototype solar-electric aircraft floats in the Pacific Ocean near the Hawaiian island of Kauai shortly after the aircraft became uncontrollable and broke up during a test flight on June 26, 2003. About 75 percent of the wreckage was recovered, but the prototype fuel cell system that was to have provided power at night during the planned long-endurance flight demonstration sank in mile-deep water and could not be recovered.