HISTORY OF FLIGHT On April 3, 1995, about 1552 central daylight time, a deHavilland DHC-8-102, N828MA, operated in commuter air carrier service by Mesaba Aviation, Inc., experienced a jammed left inboard roll spoiler during the approach to land at the Quad City Airport in Moline, Illinois. The airplane landed without damage. There were no injuries reported by the two flight crew members, one flight attendant, or the seventeen passengers on board the airplane. Visual meteorological conditions prevailed for the flight, which operated on an instrument flight rules (IFR) flight plan. The flight operated under 14 CFR Part 135, and originated from Minneapolis, Minnesota, approximately 1438. The pilots reported that the flight from Minneapolis to Moline was uneventful, until they were being vectored for the approach into the Quad City Airport. They indicated that they were cleared to descend to 4,000 feet, and assigned a heading of 110 degrees. The Captain reported that he turned the autopilot off during the left turn to the assigned heading. He stated that as he rolled out of the turn, the "...aircraft wanted to keep turning left, to level [the] aircraft I had to put about 1/3 control input to the right...I then noticed the left inboard roll spoiler was up... ." The flight crew notified Air Traffic Control (ATC) that they had a flight control problem, and declared an emergency. ATC issued vectors for the Instrument Landing System (ILS) approach to runway 27, at Moline. The Captain reported that "...the aircraft flew normally, we did not notice any unusual flight characteristics as we slowed for landing...the aircraft landed normally and all spoilers came up normally... ." The flight crew reported that although the stuck spoiler appeared to deploy to the full up position normally, it stopped at an intermediate position during retraction. Postincident inspection of the airplane revealed that the roll spoiler servoactuator, Part Number (P/N) A44700-009, had jammed in a partially deployed position. The servoactuator unit was removed for further examination (see Additional Information). AIRCRAFT INFORMATION Examination of aircraft records revealed that N828MA, a deHavilland DHC-8-102, serial number (S/N) 333, was manufactured in July, 1992. The roll spoiler servoactuator, P/N A44700-009, S/N 1756, was manufactured by MOOG, Inc., in the first quarter of 1992. The servoactuator was installed on the incident airplane by deHavilland, as original equipment. Records indicated that the airplane had about 5,849 hours total flight time, and 6,201 cycles at the time of the occurrence. Examination of maintenance logbooks revealed no evidence of previous discrepancies of the servoactuator or roll spoiler system. ADDITIONAL INFORMATION Postincident examination and disassembly of the roll spoiler servoactuator was conducted at Dowty Aerospace Los Angeles (DALA), which had purchased the servoactuator design and stock from MOOG, Inc. Disassembly of the servoactuator revealed that the plug (P/N A50993-1), which is fusion welded in the piston (P/N A50994-1) to make up the piston assembly (P/N A50992-1), had separated, and restricted the piston from full travel. DALA representatives stated that there was one previous similar occurrence, in September, 1994. Further examination revealed that the fusion weld failure originated at a defect/void in the weld. As a result of examinations conducted after the first welded plug failure, DALA representatives sent a letter to deHavilland, which stated: "Based on...testing, DALA has confidence in the integrity of the welded pistons currently in stock and intends to continue...shipping...the welded piston design until the current quantity...has been consumed. As a precaution, subsequent pistons will be manufactured per the P/N A44714-2 configuration, which is made from a swagged piston bland and does not require a welded plug." DALA representatives also stated that they believed that "...[this] type of piston failure...has no effect on the safety of the aircraft or the integrity of the hydraulic system." After the second welded plug failure, DALA issued a Service Letter to all users of DHC-8 aircraft, which advised operators of the two instances of servoactuator welded plug failures. The Service Letter recommended that "...a careful watch be maintained on the fleet for spoiler servoactuators that do not fully retract." In a letter dated June 5, 1995, the Director of Quality Assurance at DALA stated: "As a result of the second incident...[DALA] has purged its stock and scrapped...pistons with the fusion welded plug P/N A50992-1."