European Aviation Safety Agency

ATA 63 – Main Rotor Drive – Rotor Brake Pinion – Replacement
 N AD 2016-0244

Annotation

Reason:

One case was reported of a cracked rotor brake pinion, part number (P/N) 412-040-301-101, installed in the rotor brake quill P/N 412-040-123-103 of an AB412 helicopter.

This condition, if not detected and corrected, could lead to the failure of the pinion with detachment of parts inside the transmission that could cause its malfunction or jamming, finally resulting in loss of control of the helicopter.

To address this potential unsafe condition, AgustaWestland issued Bollettino Tecnico (BT) 412-135 to provide inspection instructions, and EASA issued AD 2013-0187 to require a one-time magnetic particle inspection (MPI) of the pinion and, depending on findings, replacement with a serviceable part.

Since that AD was issued, a new case of a cracked pinion has been reported. The results of the investigation revealed that this crack was due to a defect generated during the pinion manufacturing process. In agreement with EASA, Leonardo issued BT 412-147, providing instructions to identify and replace all the pinions belonging to the same manufacturing batch.

Considering the fact that only a limited number of parts is affected, it was agreed to postpone AD action, waiting for feedback from the operators of affected helicopters. Unfortunately, Leonardo received confirmation of replacement only for one pinion, out of three belonging to the affected manufacturing batch.

For the reasons described above, this AD retains the requirements of EASA AD 2013-0187, which is superseded, and requires replacing some pinions identified by serial number (s/n).