Linden Blue, originator of the Spectrum 33 VLJ and its principal investor, plans to continue development of the all-composite aircraft powered by two Williams FJ33-4 turbofans in spite of a fatal crash that claimed the lives of its two test pilots. The first and only prototype was destroyed July 25 when the aircraft's right wing struck the ground shortly after takeoff from Spanish Forks Airport, in Utah, during a routine test flight. Following the wing strike, the aircraft cartwheeled and came to rest about 750 feet from the point of initial impact.
Preliminary NTSB findings attribute the accident to incorrect rigging of the aileron linkage such that the roll controls were reversed, resulting in aileron deflections that produced a right roll when the pilot commanded a left roll. Because the control input to maintain a wings-level attitude occurred immediately after liftoff, the pilots had insufficient time to sense and adapt to the roll reversal.
The aircraft had been aloft successfully during 46 previous tests since its initial flight January 7, 2006, and June 30 when the Spectrum 33 was modified to accommodate a stiffer main gear. During that period of maintenance the aileron upper torque tube was redesigned, which required the translation linkage to be removed and subsequently reassembled. An examination of the wreckage revealed that one part had been installed backwards. During preflight and pretakeoff check procedures, the misrigging went undetected even thought the aircraft's ailerons were visible from the cockpit.
As in the case with most accidents, several factors contributed to the crash of the Spectrum 33 prototype. Similar to most roll-control systems, misrigging is possible. Redesign of the landing gear during the test program necessitated teardown and reassembly of the aileron linkage. When the aircraft was returned to flight status, maintenance and test personnel failed to detect the anomaly between control deflection and movement of the ailerons. And the test pilots apparently did not observe aileron movement when they checked for control function.
Although a promising design suffered a setback and two lives were tragically lost, there appears to be no fundamental shortcoming either in the Spectrum 33's composite construction or its highly efficient geodetic design that contributed to the accident. Spectrum Aeronautical expects to have a second prototype flying early in 2007. - John W. Olcott