The NASA mishap investigation board looking into the cause of the crash of the $15 million Helios prototype solar-electric flying wing is focusing on the electronics and flight- control system after initial indications that the unmanned craft broke up because of self-induced oscillations.

The 75m (247ft)-span remotely piloted Helios plunged into the Pacific Ocean 18km (10nm) west of the Hawaiian island of Kauai last month after it "experienced control difficulties that resulted in severe oscillations". The abrupt manoeuvring at around 3,000ft led to structural damage and the subsequent crash. By 2 July, more than 75%, by weight, of the aircraft had been recovered from the water, but NASA says the $10 million, 335kg (750lb) fuel cell system sank and "will not be recovered". The sea depth at the site in the US Navy's Pacific Missile Range Facility is about 1,800m.

The AeroVironment-built Helios, powered by electricity generated by an advanced experimental fuel cell, was on a checkout flight for a planned 40h endurance demonstration and was due to draw power from its fuel cell for the first time (Flight International, 17-23 June).

Source: Flight International