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Tue, Aug 01, 2006

NTSB: Spectrum 33 Controls Misrigged In Fatal Accident

ANN REALTIME REPORTING 08.02.06 1800 EDT: The National Transportation Safety Board has just released its Preliminary Report on last week's fatal accident involving the prototype Spectrum 33 very-light-jet in Utah.

In its report -- which is published in its entirety below -- the NTSB says the aircraft's ailerons were apparently misrigged... so that control inputs for roll control would have had the opposite effect than the plane's pilots intended.

"Examination of the translation linkage on the aft side of the aft pressure bulkhead revealed that it was connected in a manner that reversed the roll control," say the Prelim. "Specifically, the linkage was connected such that left roll input from the side sticks would have deflected the ailerons to produce right roll of the airplane, and right roll input from the side sticks would have deflected the ailerons to produce left roll of the airplane."

The NTSB also reports the airplane had undergone maintenance prior to the accident, during which time the main landing gear was removed in order to stiffen the struts. When workers reinstalled the MLG, the NTSB says they found the modifications resulted in inadequate clearance between the left MLG strut, and the aileron upper torque tube V-bracket. The V-bracket was removed and redesigned to allow proper clearance of the gear... which also required a portion of the aileron linkage to be removed, and subsequently reinstalled.

Witnesses report the aircraft entered a right roll just as the plane was lifting off from runway 30 at Spanish Fork-Springville Airport in Spanish Fork, UT in July 25. As Aero-News reported, Spectrum's Glenn Maben and Nathan Forrest were lost in the accident.

NTSB PRELIMINARY REPORT

On July 25, 2006, approximately 1606 mountain daylight time, a Spectrum 33 experimental twin-engine jet airplane, N322LA, collided with terrain following a loss of control during the initial climb after takeoff from runway 30 at Spanish Fork-Springville Airport, Spanish Fork, Utah. The airplane, which was registered to and operated by Spectrum Aeronautical LLC, was destroyed by impact forces. The two commercial pilots aboard received fatal injuries. Visual meteorological conditions prevailed and no flight plan was filed for the 14 CFR Part 91 local maintenance test flight. The flight was originating when the accident occurred.

Witness observations indicate that the airplane entered a right roll almost immediately after takeoff. The roll continued to about 90 degrees right wing down when the right wingtip impacted the ground.

Examination of the accident site revealed that the initial impact point was located about 150 feet right of the runway 30 centerline. A ground scar oriented on a magnetic heading of about 330 degrees extended from the initial impact point to a barbed wire fence about 120 feet away. Various pieces of right wing debris were found along the ground scar. The wreckage path veered about 20 degrees right at the fence and then remained essentially straight to the main wreckage site on about a 350 degree magnetic heading. The main wreckage was located about 750 feet from the initial impact point and included the forward fuselage, aft fuselage and a majority of the wing structure. All major components of the airplane were accounted for in the wreckage path or with the main wreckage. There was no evidence found of any pre-existing failures of the airplane's structure.

Roll control on the airplane was from the pilots' side sticks to the ailerons through a mechanical system of torque tubes and push-pull tubes. The left side stick was primary, and the right side stick was slaved to the left side stick. The roll control motion of the left side stick was linked through a quadrant below the cockpit floor to the lower torque tube. The lower torque tube ran from the quadrant to the aft pressure bulkhead. The translation linkage, the linkages and bell cranks that translated the rotational motion of the lower torque tube to a linear motion of the aileron push-pull tubes, was located on the aft side of the pressure bulkhead in the main landing gear (MLG) gearbox area.

During examination of the wreckage, aileron control continuity could not be established from the cockpit to the aft pressure bulkhead due to fragmentation of the airplane, however, all of the lower torque tube was accounted for. Control continuity was established from the torque tube input on the aft pressure bulkhead to the aileron bellcrank on the right wing and to the torque tube about 50 inches inboard of the aileron bellcrank on the left wing. Examination of the translation linkage on the aft side of the aft pressure bulkhead revealed that it was connected in a manner that reversed the roll control. Specifically, the linkage was connected such that left roll input from the side sticks would have deflected the ailerons to produce right roll of the airplane, and right roll input from the side sticks would have deflected the ailerons to produce left roll of the airplane.

According to information provided by the operator, the airplane had accumulated about 44 hours total flight time since its first flight on January 7, 2006. Prior to the accident flight, the airplane's most recent flight, flight number 46, had taken place on June 30, 2006. During the time between flight 46 and the accident flight, the airplane had been undergoing maintenance. The maintenance included removal of the MLG in order to stiffen the MLG struts. Upon reinstallation of the MLG, it was found that inadequate clearance now existed between the left MLG strut and the aileron upper torque tube V-bracket. The V-bracket was removed and redesigned to allow proper clearance of the MLG. Removal of the V-bracket required disconnection and removal of a portion of the translation linkage.

FMI: www.ntsb.gov, www.spectrum.aero

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