The November 2006 fatal crash of the Grob G180A SPn prototype was caused by failure of the twinjet’s horizontal stabilizer, according to the final report recently issued by the German Federal Bureau of Aircraft Accident Investigation (BFU). “The wreckage pattern allowed for only one conclusion: that the horizontal stabilizer had suffered an in-flight breakup due to aerodynamic flutter,” rendering the aircraft uncontrollable, the report stated. While the cause of the flutter was not determined, investigators considered a retrofitted elevator mass balance a possible culprit, as well as prior damage to the elevator horn. The company’s chief pilot was killed in the crash, which occurred while the SPn was being flown on a demonstration flight in low ceilings. Company policy dictated a “reduced flight display”–speed below 200 knots and a cloud-base minimum of 1,500 feet–but the aircraft was flying at up to 270 knots. The BFU issued several safety recommendations stemming from the accident, including a requirement that all test aircraft with an mtow of more than 12,566 pounds be equipped with flight data and cockpit voice recorders. The agency also wants EASA and other civil aviation authorities to “check and monitor the integration of subcontractors in design organizations engaged in the design and construction of aircraft.”