Summary
We propose to adopt a new airworthiness directive (AD) for the products listed above that would supersede an existing AD. 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. The MCAI describes the unsafe condition as:
Two reports have been received where, during inspection of the vertical stabilizer of F28 Mark 0100 aeroplanes, one of the bolts that connect the horizontal stabilizer control unit actuator with the dog-links was found broken (one on the nut side & one on the head side). In both occasions, the bolt shaft was still present in the connection and therefore the horizontal stabilizer function was not affected. If a single dog-link connection fails, the complete stabilizer load is taken up by the remaining dog-link connection. * * *
To address and correct this unsafe condition EASA [European Aviation Safety Agency] issued AD 2007-0287 [corresponding FAA AD 2008-22-14] that required a one-time inspection of the affected bolts, * * * and replacement of failed bolts with serviceable parts. EASA AD 2007-0287 also required the installation of a tie wrap through the lower bolts of the horizontal stabilizer control unit, to keep the bolt in place in the event of a bolt head failure. Recent examination revealed that the bolts failed due to stress corrosion, attributed to excessive bolt torque. Investigation of the recently failed bolts showed that the modification as required by AD 2007-0287 is not adequate. * * * * * Loss of horizontal stabilizer function could result in partial loss of control of the airplane. The proposed AD would require actions that are intended to address the unsafe condition described in the MCAI.