The fatal 2003 crash of a prototype Sino-Swearingen SJ30-3 business jet during high-speed flutter testing was probably caused by the manufacturer's incomplete high-Mach design research, says the US National Transportation Safety Board (NTSB). As a result, the aircraft became unstable and diverged into an uncontrollable roll (Flight International, 27 May–2 June 2003).
The company had not conducted any high-speed windtunnel testing before the accident, in which the pilot lost lateral control while in a descent to attain a M0.884 target speed during a flutter test. The manufacturer's engineering analysis predicted positive lateral stability up to M0.9, but high-speed windtunnel testing conducted after the crash found the aircraft became laterally unstable above M0.83, the NTSB says.
Source: Flight International