Helios Investigation Team wraps up Field Work - Analysis Begins

source: NASA Dryden 2003.7.10

The NASA Mishap Investigation Board (MIB) that is probing the causes of the in-flight mishap that led to the loss of the Helios Prototype solar-electric aircraft June 26 has completed the on-site portion of their task at the U.S. Navy's Pacific Missile Range Facility (PMRF) on the Hawaiian island of Kauai, and will now turn towards coming up with a probable cause of the accident.

While the investigation is continuing, both NASA and Helios manufacturer and operator AeroVironment, Inc., are moving ahead with planning for follow-on activity to mature the solar and fuel cell propulsion systems technology developed for the Helios, while incorporating lessons learned from the mishap investigation in the planning effort.

An interim status report released by the Mishap Investigation Board July 8 indicates the Helios Prototype appeared to have experienced undamped pitch oscillations that led to a partial breakup of the aircraft in mid-air while flying at about 3,000 feet altitude in restricted test range airspace over the Pacific Ocean about 10 miles west of Kauai. The Helios Prototype had been aloft for about a half-hour on the second of two checkout flights leading to a planned long-endurance flight demonstration later this summer, using power from its solar arrays by day and from an experimental fuel cell system at night. The fuel cell system had not yet been turned on when the mishap occurred.

According to the interim status report, the board believes the undamped pitch oscillations may be related to the complex interactions between the aerodynamic, structural, stability and control and propulsion systems on a flexible aircraft. However, the board emphasized that this hypothesis is still preliminary, and much work needs to be done to discover the primary causes of the mishap.

The five-member board led by Dr. Thomas E. Noll of NASA Langley Research Center completed their field work July 7. During their nine days at PMRF where the Helios Prototype was based during the summer flight deployment, the team collected all of the "perishable data," including witness interviews and statements, reviewed available program information, developed a fault-tree analysis, and developed several potential contributing causes to the mishap. The board's investigation is being aided by good telemetry data received during the flight, as well as video and still photos that recorded much of the incident from a chase helicopter.

Over the next few weeks, the team, assisted by several ex-officio members and support staff from NASA Dryden Flight Research Center and AeroVironment, Inc., will continue reviewing available data, initiate independent analyses and tests to further investigate certain technical areas, and will begin drafting parts of the mishap report. The board will reconvene at AeroVironment's facility in Simi Valley, Calif., the first week in August to review the independent analysis and to further develop possible causes, recommendations and lessons learned.

AeroVironment's Helios team has also begun a parallel investigation into the possible causes of the mishap and will be providing input to the MIB as it progresses through its independent effort. The MIB's final report is due by Sept. 30.

About three-fourths of the Helios Prototoype wreckage has been recovered from the ocean, and will be shipped to California in the near future to aid in further investigation of the accident.

"The Helios Prototype project has made great strides in advancing the technology of solar-powered aircraft, as evidenced by the record altitude flight in 2001," commented John Del Frate, Helios project manager at NASA Dryden. "The value of the program is not only in development of the aircraft platform, but in the related technologies, i.e., solar and fuel cell systems, for both airborne and terrestrial applications. We will use results of the accident investigation to improve the next generation of the Helios."

Based on requirements of NASA, Defense Department, and commercial users of future extreme-duration aircraft, the effort will focus on investment in technology development and demonstration of extreme-duration UAV flight in the stratosphere, added Bob Curtin, vice president in charge of Aerovironment’s UAV Design Development Center.

"The plan will get a jump start from the fuel cell and electric propulsion technologies developed for Helios and its predecessors," said Curtin. "Although saddened by the loss of Helios, the AeroVironment team will respond to the loss as a challenge to learn from the incident and incorporate Helios technologies into a new and better extreme-endurance UAV.”