AD NUMBER: 2011-08-05

MANUFACTURER: Airbus Model A310 Series Airplanes; and Model A300 B4-600, A300 B4-600R, A300 F4-600R Series Airplanes, and Model A300 C4-605R Variant F Airplanes (Collectively Called A300-600 Series Airplanes)
SUBJECT: Airworthiness Directive 2011-08-05

SUMMARY: This AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as:

The ball screw nut assemblies of the first 70 Trimmable Horizontal Stabilizer Actuators (THSA) manufactured by Goodrich were fitted with an upper attachment gimbal having a thickness of 58 mm (2.28 in), which is different from the design of the final production standard. The gimbal installed on the subsequent THSAs (final production standard) is more robust, having a thickness of 70mm (2.76 in).

During the fatigue life demonstration of the THSA upper attachment primary load path elements, only a gimbal having a thickness of 70mm (2.76 in) was used. Thereafter, no additional justification work to demonstrate the robustness of the upper attachment fitted with a gimbal of 58 mm was accomplished. In case of failure of this gimbal, the THSA upper attachment primary load path would be lost and the THSA upper attachment secondary load path would engage.

Because the upper attachment secondary load path will only withstand the loads for a limited period of time, the condition where it would be engaged and not detected could lead to failure of the secondary load path, which would likely result in loss of control of the airplane.

FMI: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/4A83EE30CAAE6375862578790051C638?OpenDocument