7 July 1999
Cracked pitch link nuts
During an unscheduled inspection of a 206 BIII helicopter, four pitch link nuts (P/N MS35691-29 and -33) were reported to have cracked. Five more nuts were removed from the operator's aircraft as a result of a thorough inspection of the fleet. In total, seven nuts were collected: some were found cracked and others showed only a small surface discontinuity, which could be attributed to the manufacturing process. Corrosion was present on all nuts. The operator confirmed that the required corrosion prevention compound, MIL-C-16173 Grade 1, was applied as per the applicable maintenance procedures.
As a result of a related article on the subject in Feed-Back 3&4/98, three more cracked nuts were found during inspection of another operator's fleet. While it was difficult to determine the nature of the crack initiation, lab investigation concluded that the cracks could have been induced by overtorquing during installation.
Transport Canada recommends a close inspection of all pitch link nuts for cracks during the scheduled 100-hour inspections for condition and security.
Any defects or further occurrences should be reported by sending a Service Difficulty Report to Transport Canada, Continuing Airworthiness, Ottawa.
For further information contact a Transport Canada Centre, or call Mr. Bogdan Gajewski, Continuing Airworthiness, Ottawa, telephone (613) 952-4450, facsimile (613) 996-9178 or e-mail email@example.com.
For Director, National Aircraft Certification
Chief, Continuing Airworthiness