CHARLESTON, WV, USA
N852MA
de Havilland DHC-8-102
The captain said that during takeoff rotation, the airplane rolled left. He noted no warning lights or horns before or during the event. He applied right control wheel and right rudder to stop the left roll. After the captain had the airplane's roll stabilized, he 'made a wide left pattern and returned to the departure airport.' The airplane was landed without further incident. A postincident inspection of the airplane revealed that the left inboard roll spoiler was 'jammed and partially deployed.' An examination and disassembly of the roll spoiler servoactuator revealed that a plug (PN A50993-1), which had been fusion-welded into the base of the piston (PN A50992-1), had separated and lodged between the base of the piston and the shims, restricting the piston's movement. Dowty Aerospace (the manufacturer) had recorded six previous failures of fusion welds in pistons on DHC-8 roll spoiler servoactuators before this incident.
HISTORY OF FLIGHT On January 22, 1997, at 0910 eastern standard time (est), a Dehavilland DHC-8-102, N852MA, operated as Mesaba Flight 3098, by an airline transport pilot, experienced an uncommanded left rolling bank just after takeoff. The pilot corrected the situation and the airplane was landed at Yeager Airport, Charleston, West Virginia, without further incident. Post-flight examination of the left wing revealed that the left inboard roll spoiler was extended half-way. Visual meteorological conditions prevailed at the time of the incident. The flight was being conducted as domestic commuter air carrier service under 14 CFR Part 121. An IFR flight plan was on file. There were no reported injuries by the two flight crew members, one flight attendant or eight passengers on board the airplane. The flight originated at Charleston, West Virginia, at 0910 est, and was en route to Roanoke, Virginia. In his written statement, the captain said during the takeoff rotation, the airplane rolled left. The captain noted no warning lights or horns prior to, or during the event. The captain applied right control wheel and right rudder to stop the left roll. After the captain had the airplane's roll stabilized, he "made a wide left pattern and returned to the departure airport." The crew continued their climb to 10,000 feet mean sea level (MSL). On their return to Charleston, West Virginia, the crew attempted to depressurize the actuator using the roll spoiler pressure switch. This had no effect on the control of the airplane. The captain landed the airplane without further incident. AIRCRAFT INFORMATION The airplane, a Dehavilland DHC-8-102, serial number 349, had undergone a line check inspection on January 19, 1997. At the time of the incident, the airplane had 9,665 total flight hours. A post-incident inspection on the airplane was conducted by Mesaba Airlines Maintenance at Charleston, West Virginia, on January 22, 1997. The examination revealed that the left inboard roll spoiler was "jammed and partially deployed." The roll spoiler servoactuator (part number A44700-009) was removed and retained for further testing. TESTS AND RESEARCH An examination and disassembly of the roll spoiler servoactuator (serial number 1743) was conducted at Dowty Aerospace, Duarte, California on April 29, 1997. The roll spoiler servoactuator was manufactured by Dowty Aerospace in the first quarter of 1992. Disassembly of the servoactuator revealed that the plug (part number A50993-1), which is fusion-welded into the base of the piston (part number A50992-1), had separated and lodged itself between the base of the piston and the shims, restricting the piston's movement. Dowty Aerospace had recorded six previous failures of fusion welds in pistons on DHC-8 roll spoiler servoactuators prior to this incident. The first failure was reported by Horizon Air, Incorporated, in August, 1994, when a roll spoiler servoactuator malfunctioned during a check of the airplane's flight controls on the ground. The second failure occurred on a Mesaba Airlines DHC-8, N828MA on April 4, 1995. Between June 5, 1995, and January 20, 1997, eight additional roll spoiler servoactuators with the fusion welded piston design were returned to Dowty Aerospace by DHC-8 operators. Four of the eight units had failed welds around the piston plugs. Dowty Aerospace sent the piston from the Horizon Air servoactuator to M. M. A. Laboratories, Huntington Beach, California, for failure analysis on September 1, 1994. Results of the analysis confirmed failure in the fusion weld. Dowty Aerospace then conducted impulse testing on three randomly selected pistons from their stock. The pistons were subjected to 50,000 cycles at 0 to 3,000 pounds per square inch (psi) at rates of 0.5 seconds at 0 psi, to 2 seconds at 3,000 psi. A magnetic particle inspection following the testing revealed no cracks in the welds. Following the second operational failure of a piston plug fusion weld, Dowty Aerospace issued a service letter to all DHC-8 operators informing them of the weld failures and requested that these operators monitor their fleets for similar problems. On March 31, 1995, Dowty Aerospace converted its manufacturing of their roll spoiler servoactuators to incorporate a new piston which did not require a welded plug. On May 31, 1995, Dowty Aerospace scrapped its stock of 41 pistons which had the fusion welded plug. ADDITIONAL INFORMATION Parties to the investigation were the Federal Aviation Administration, the Transportation Safety Board of Canada, Dowty Aerospace Los Angeles, and Mesaba Airlines.
a fractured fusion weld in the piston of the roll spoiler servoactuator, which allowed the plug at the base of the piston to separate and jam the piston. A factor relating to the incident was: the inadequate design of the airplane's roll spoiler servoactuator piston.
Source: NTSB Aviation Accident Database
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