The FAA has issued Special Airworthiness Information Bulletin CE-19-19 (SAIB) recommending that operators of all model Mitsubishi MU-2 twin turboprops comply, if they have not already, with three-year-old manufacturer’s Service Bulletins (SBs) that outline procedures to detect and correct cracks in the wing spacer plates. If left uncorrected, these cracks could result in reduced structural integrity of the wings, the FAA said, but added, “At this time, the airworthiness concern is not an unsafe condition that would warrant Airworthiness Directive (AD) action.”
As part of the MU-2B aging aircraft program, one-piece and three-piece main wings were subjected to detailed teardown inspections, and cracks were found in the wing spacer plates attached to the forward lower spar area at wing station 580. It was determined that the cracks resulted from fatigue caused by flight loads.
To address this, Mitsubishi issued MU-2 Service Bulletin No. 245, dated April 21, 2016, and MU-2 Service Bulletin No. 107/57-005, dated May 3, 2016. These SBs describe procedures for performing a fluorescent penetrant inspection of the wing spacer plates for cracks and replacing cracked wing spacer plates with an improved part.
The FAA is urging owners and operators to follow these guidelines, but agency officials could not be reached by AIN at press time to comment if a low rate of compliance or other factors led to the SAIB issuance.