Incident Summary
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.
Examination Findings
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."
Maintenance and Testing
A 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 measures the aileron surface position, was one of the checked parameters. To verify accuracy, the left control wheel is rotated until the ailerons contact their stops, and the FDR roll control parameter value is compared to an approved limit. The mechanic who conducted the check reported it was routine. Analysis of available FDR data from the incident flight and over 83 preceding flights showed that the maximum values recorded for the 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 TED value was not within the range required by the approved operator's B1900D maintenance inspection procedures. During the functional check, the maximum roll parameter values exceeded previous maxima by 1.9 degrees in TED and 1.0 degree in TEU, marking the only time both values were within the required TED range.
The aircraft manufacturer and NTSB tested the aileron control system on an exemplar Beechcraft 1900D aircraft in Wichita to determine the tangential force required to change the roll parameter by 1.9 degrees in TED. Results showed that an additional 80 pounds of tangential force, applied after the aileron rested against its stop, increased the parameter by 0.7 degrees in TED and 1.3 degrees in TEU. No further force was applied because the limit load for the aileron control system is 80.4 pounds. An engineering report showed that the aileron system did not yield at the limit load (80.4 pounds) or fail at the ultimate load (120.6 pounds). The aileron control system, including the brazed joint, met all FAA 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.