CHI03IA153

The flight crew of the incident aircraft reported lateral control problems shortly after takeoff, noting that about 45 degrees of right control wheel deflection was required to maintain straight flight. They noted no other anomalies and seemed to have full flight control authority. However, as a precaution, the flight crew elected to return and land at the departure airport. The crew reported that the landing was normal with the exception of the required control wheel offset. A post incident examination of the aileron control system revealed a 360º fracture in the silver-brazed joint between the drive sprocket and its mating shaft of the left-hand aileron control sprocket assembly. The failure of the brazed joint allowed both control wheels to be rotated approximately 45 degrees from neutral without a corresponding aileron control surface response. NTSB metallurgical examination of the left-hand sprocket assembly revealed that it was not brazed according to the referenced specifications. Specifically, the examination noted that the braze filler material had been introduced from both ends of the joint, resulting in a lack of penetration of about 20 percent of the total joint area. The applicable specification states, "the filler metal shall be introduced at one edge...and shall flow by capillary action to fill the interstice." The NTSB's review of the incident aircraft's maintenance records showed that a flight data recorder (FDR) functional check was completed the night before the incident flight. The roll control parameter, which is designed to measure the aileron surface position, was one of the parameters checked. To verify the accuracy of this parameter, the left control wheel is rotated either clockwise or counterclockwise until the ailerons contact their respective up or down stops. When the stops are contacted, the control wheel is held in position and the FDR roll control parameter value is checked against an approved maintenance manual limit. The control wheel is then rotated in the opposite direction and the FDR parameter is verified. The mechanic who conducted the functional check reported that the FDR functional check was routine. NTSB analysis of available recorded FDR data, incident flight and over 83 flights before the incident flight, showed that the maximum values recorded for the FDR roll control parameter prior to the functional check were 14.6 degrees aileron trailing edge down (TED) and 23.4 degrees aileron trailing edge up (TEU). The recorded aileron TED value was not in the range required by the approved operators B1900D maintenance inspection procedures document. The analysis also showed that, during the FDR functional check, the maximum values recorded for the roll parameter exceeded the maximum values recorded prior to the incident by 1.9 degrees in the aileron TED direction and 1.0 degree in the aileron TEU direction. This was the only time that both FDR values for the roll control parameter were in the TED range required by the functional check. The aircraft manufacturer and the NTSB tested the aileron control system on an exemplar Beechcraft 1900D aircraft in Wichita. The purpose of the test was to determine the amount of tangential force, applied to the control wheel, required to change the FDR roll control parameter value by 1.9 degrees in the aileron TED direction. Results of the testing showed that an additional tangential force of 80 pounds applied to the control wheel, after it was rotated such that an aileron was resting against its control surface stop, increased the roll parameter value by 0.7 degrees in the aileron TED direction and 1.3 degrees aileron TEU. Additional force was not applied to the control wheel because the limit load for the aileron control system is 80.4 pounds. The airplane manufacturer provided a Beechcraft 1900D Engineering report that documented tests that were conducted on the aileron control system to demonstrate compliance with the Code of Federal Regulations. Test data show that the aileron system did not yield while applying a limit tangential load of 80.4 pounds to the control wheel or fail when an ultimate tangential load of 120.6 pounds was applied to the control wheel. The aileron control system, including the brazed joint on the sprocket assembly, met all Federal Aviation Administration airworthiness standards for commuter-category aircraft. The investigation concluded that the failed sprocket assembly significantly reduced the pilots' control of the ailerons because the failure affects pilot input from both control wheels.

History of flight

On June 7, 2003, approximately 1400 central daylight time, a Beech (Raytheon) 1900D, N901SK, operated by Skyway Airlines Inc. as flight 1233, experienced lateral control problems shortly after takeoff from General Mitchell International Airport (MKE), Milwaukee, Wisconsin. An emergency was declared and the flight returned to MKE, landing without incident at 1410. The two crewmembers and six passengers reported no injuries. Visual meteorological conditions prevailed at the time of the incident. The flight was conducted under 14 CFR Part 121 and was on an instrument flight rules (IFR) flight plan. The flight departed MKE at 1345 with an intended destination of Sawyer International Airport (SAW), Gwinn, Michigan.

According to the captain's written statement, immediately after takeoff the first-officer, who was the pilot flying, announced that approximately 45-degrees of right control wheel deflection was required to maintain straight flight. The captain reported they climbed to 7,000 feet mean sea level in order to evaluate the problem. He stated: "We then elected to make several maneuvers at altitude to determine whether we had full flight control authority. No anomalies were evident." He reported that after notifying air traffic control and Skyways operations of the situation, they elected to return to MKE for a precautionary landing. Concerning the approach and landing, the captain noted: "We elected to perform a no flap landing, since we had no idea what was causing the anomaly. Approach and landing were normal other than the required yoke deflection needed the entire time."

Airline maintenance personnel conducted a post-incident inspection of the aileron system. According to their statement, the aileron system rig pin was installed in an attempt to isolate the problem. The aileron control surfaces were aligned at the neutral (zero deflection) position indicating the problem was between the rig pin and the control wheels. The mechanics reported that closer inspection of the system revealed that the captain's (left side) aileron control column sprocket assembly was cracked at the silver braze between the aileron drive sprocket and the shaft. This allowed both control wheels to be rotated without corresponding movement of the aileron control surfaces.

Personnel information

The pilot-in-command (PIC) held an Airline Transport Pilot (ATP) certificate with single and multi-engine land ratings. Single-engine operations were limited to commercial pilot privileges, according to Federal Aviation Administration (FAA) records. The certificate listed a type rating for the BE-1900, with a limitation stating "BE-1900 Second in Command Required."

The PIC held a First Class medical certificate issued on May 27, 2003. This certificate listed a restriction stating: "Must wear corrective lenses." He had accumulated approximately 3,400 hours total time. His most recent 14 CFR Part 121 training event was on May 7, 2003.

The second-in-command (SIC) held an ATP certificate with single and multi-engine land ratings. Single-engine operations were limited to commercial pilot privileges, according to FAA records. The certificate listed a type rating for the BE-1900, with a limitation stating "BE-1900 Second in Command Required."

The SIC held a First Class medical certificate issued on October 21, 2002. This certificate listed a restriction stating: "Must wear corrective lenses for near and distant vision." He had accumulated approximately 3,920 hours total time. His most recent 14 CFR Part 121 training event was on July 16, 2002.

Aircraft information

The incident aircraft was a 1994 Beech (Raytheon) 1900D Airliner. Skyway Airlines was operating the aircraft in 14 CFR Part 121 revenue service at the time of the incident. The 1900D is a twin-engine, turbo-prop, pressurized aircraft certified to 14 CFR Part 23 Commuter Category regulations through Amendment 34.

The aircraft was issued an airworthiness certificate on March 29, 1994. According to the operator, it had accumulated 20,720 hours total time over 25,472 cycles. The most recent maintenance inspection under the operator's continuous airworthiness program was completed on May 28, 2003, at 20,678 hours.

According to maintenance records, the night before the incident flight a flight data recorder (FDR) functional check was completed. The mechanic who conducted the functional check reported the procedure was routine. He stated that no discrepancies were noted, the FDR performed per the specification and the aircraft was approved for return to service.

The incident flight was the first flight of the day. According to the MKE chief pilot, the same crew assigned to the incident flight preformed the first flight of the day checks. He reported no anomalies were found during those checks.

The 1900D lateral control system consists of a direct mechanical connection via control cables between the Captain's and First Officer's control wheels and the aileron control surfaces. The primary elements of this system are the control wheels, sprocket assemblies, connecting cables, bellcranks, pushrods and ailerons.

Meteorological information

Weather conditions at MKE, recorded at 1352, were: scattered clouds at 6,000 feet above ground level (agl), scattered clouds at 7,500 feet agl, 4 statute miles visibility in haze, and winds from 130 degrees at 11 knots.

Tests and research

The captain's (left side) control wheel torque tube was connected to the Aileron Sprocket Assembly (Raytheon Part No.: 100-524120-1) through a universal joint. The sprocket assembly consisted of a shaft and two sprockets. Each sprocket was silver brazed to the shaft.

Raytheon engineering drawing, Sprocket Assembly - Control Column, Aileron, No.: 100-524120, dated 2/28/1972, specified the braze operation to be in accordance with MIL-B-7883. A general note required that the completed assembly be proof loaded prior to acceptance. Specifically, a 3,619 lbs. axial load was to be applied to the shaft and resisted at the sprocket. After testing a proof stamp was required to be applied to the part. The proof stamp was present on the incident part.

An engineering change order was issued which revised the braze note to read: "Silver braze per spec MIL-B-7883 except omit paragraph 4.4.2 radiographic inspection." A general note was added to the drawing at that time which stated: "Visually inspect to see that the braze material has filled the joints between shaft and all mating silver brazed parts 100%." According to the order, the change was initiated because the assembly configuration "does not lend itself to radiographic inspection."

Military Specification MIL-B-7883B which specifies requirements for brazing steels states: "The filler metal shall be introduced at one edge ... and shall flow by capillary action to fill the interstice." The specification also requires removal of flux residue immediately after brazing and cooling. No residual flux is permitted on the surface of the brazed joint per the specification. Any lack of penetration is cause for rejection of the part.

The specification also states that internal defects that do not exceed 15% of the joint area, either collectively for multiple small defects or singly for one large defect, are permitted.

The specification denotes two grades for joint quality. Grade A is applicable for "critical fittings and structural applications." Critical fittings are defined as ones in which "the single failure of which would cause significant danger to operating or other personnel or would result in a significant operational penalty." This is further clarified to specifically include loss of control of an aircraft. The quality assurance inspection required for a Grade A joint includes visual and radiographic examination, as well as a dimensional inspection.

Raytheon Process Standard PS 35010D, Silver Alloy