Summary
We propose to adopt a new airworthiness directive (AD) for the products listed above. This proposed 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. For Model A310 and A300-600 series airplanes, the MCAI describes the unsafe condition as:
Hamilton Sundstrand (HS), the manufacturer of the RAT [ram air turbine], reported the failure during a wind tunnel test of a balance weight fastening screw on the RAT turbine cover. After investigation, it has been discovered that a batch of screws, which are used to attach the balance washers of the HS RAT Turbine Assembly, has not been subject to the correct heat treatment and are consequently exposed to potential fracture.
This condition, if not corrected, might lead to the ejection of screw heads and consequently to the detachment of the associated balance washers. The loss of balance washers could increase RAT vibrations, which might lead to a possible detachment of RAT parts and consequent loss of RAT functionality. The loss of the RAT, in combination with a total engine flame out, could result in loss of control of the aeroplane.
* * * * *
For Model A318, A319, A320, and A321 series airplanes, the MCAI describes the unsafe condition as:
Hamilton Sundstrand (HS) reported the failure of a balance weight fastening screw on the RAT turbine cover during a wind tunnel test. After investigation, it has been discovered that a batch of screws, used to attach the balance washers of the RAT Turbine assembly, has not received the correct heat treatment, making them more subject to a potential failure.
This condition, if left uncorrected, could lead to the ejection of screw heads and detachment of the associated balance washers. The loss of balance washers would increase RAT vibrations, which could lead to a possible detachment of RAT parts and loss of RAT functionality. The loss of the RAT, in combination with a double engine failure, or a total loss of normal electrical power generation, could result in loss of control of the aeroplane.
* * * * *
For Model A330 and A340 series airplanes, the MCAI describes the unsafe condition as:
Hamilton Sundstrand (HS), the manufacturer of the RAT, reported the failure of a balance weight fastening screw on the RAT cover during a wind tunnel test. After investigation, it has been discovered that a batch of screws, which are used to attach the balance washers of the HS RAT turbine lower gear box assembly, has not been subject to the correct heat treatment and the screws are consequently exposed to potential fracture.
This condition, if not corrected, might lead to the ejection of screw heads and consequently to the detachment of the associated balance washers. The loss of balance washers could increase RAT vibrations, which might lead to a possible detachment of RAT parts, and thus todamage to the aeroplane and risk of injury to persons on the ground.
* * * * *
The proposed AD would require actions that are intended to address the unsafe condition described in the MCAI.