N901SK

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 Brazed Joints in Primary Structures (12/05/1952), concerning the placement of filler metal, stated: "If no [joint filler] grooves are specified, the filler metal shall be placed at the edge or end of the joint, or manually fed into the joint during the brazing operation."

The sprocket assembly and the Flight Data Recorder (FDR) were removed and sent to National Transportation Safety Board (NTSB) laboratory facilities for examination. The complete Materials Laboratory and Vehicle Recorders Laboratory Factual Reports are contained in the docket material associated with this report.

NTSB Materials Laboratory examination of the sprocket assembly removed from the incident aircraft revealed a 360-degree fracture on both sides of the braze joint between the larger aileron cable sprocket and the shaft. When the sprocket was removed from the shaft it separated freely, with no ligaments of the braze still intact.

Visual examination noted that filler material had been introduced from both sides of the joint and that the two braze regions did not meet at any point around the circumference of the joint. A lack of penetration of braze filler material was observed over approximately 20% of the joint area. Separation appeared to be at the braze-to-shaft and braze-to-sprocket interfaces. Minimal fracturing through the braze material was observed. Dimensional inspection of the components did not reveal any discrepancies when compared to the drawing requirements.

In addition to the sprocket from the incident aircraft, three additional sprocket assemblies were reviewed for comparison. These assemblies were obtained from: (1) Air Midwest Beech 1900 accident aircraft at Charlotte, North Carolina (NTSB No.: DCA03MA022); (2) Colgan Airways Beech 1900 accident at Yarmouth, Massachusetts (NTSB No.: NYC03MA183); and (3) CommuteAir Beech 1900 in-service aircraft.

The sprocket assembly from the Air Midwest Beech 1900 appeared cracked at the aft sprocket-to-shaft braze joint over approximately 350-degrees of the circumfere...