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. The MCAI describes the unsafe condition as:
Incomplete accomplishment instructions in SB [service bulletin] ATR72-27-1059 original issue and Revision 1, failed to mention installation of cotter pins to secure the self locking nuts after re-installation of the modified Pitch Uncoupling Mechanism (PUM), when connecting the elevator control linkage rods to the PUM input levers and the PUM output rods to the elevator bellcranks (on both sides). Because of the non-installation of these four cotter pins, the fail-safe criteria of the design requirements on the pitch control are no longer met. Such a failure could cause the loss of one self locking nut and would result in the loss of pitch control on one side--Captain or First Officer--or the loss of control of one elevator surface. The symmetrical loss of two concerned self-locking nuts could lead to a complete loss of the pitch control. * * * * *
The proposed AD would require actions that are intended to address the unsafe condition described in the MCAI.