AD requires high frequency eddy current testing
Significant Comments in the Docket
Winglet and other new tech ?
US regulators are ordering operators of winglet-equipped Boeing 767-300s to conduct checks on the wing structure following occurrences of fatigue cracking.
This AD was prompted by reports of fatigue cracking on airplanes with Aviation Partners Boeing winglets installed. This AD requires high frequency eddy current (HFEC) inspections for cracking of the lower outboard wing skin, and repair or modification if necessary. This AD also requires one of three follow-on actions: Repeating the HFEC inspections, modifying certain internal stringers and oversizing and plugging the existing fastener holes of the lower wing, or modifying the external doubler/tripler and doing repetitive post-modification inspections. We are issuing this AD to address the unsafe condition on these products. DATES: This AD is effective July 10, 2018.
The Boeing Company Model 767–300 and –300F series airplanes. The NPRM published in the Federal Register on June 5, 2015 (80 FR 32066). The NPRM was prompted by reports of fatigue cracking on airplanes with Aviation Partners Boeing winglets installed.
We issued an SNPRM to amend 14 CFR part 39 by adding an AD that would apply to certain The Boeing Company Model 767–300 and –300F series airplanes. The SNPRM published in the Federal Register on November 27, 2017 (82 FR 55958). The SNPRM proposed adding new HFEC inspections for cracking of an expanded area of the lower outboard wing skin for certain airplanes. We are issuing this AD to address fatigue cracking in the lower outboard wing skin, which could result in failure and subsequent separation of the wing and winglet and consequent reduced controllability of the airplane.
RIN 2120–AA64 Airworthiness Directives;
The Boeing Company Airplanes
The AD is directed at 300 B-767-300s with Aviation Partners Boeing winglets installed operated by American Airlines, Delta Air Lines, United Airlines and UPS. The carriers must subject the aircraft to high-frequency eddy-current inspections for cracking of the lower outboard wing skin on the modified aircraft. The same Part 39 amendment instructs the operators to perform repeat inspections, modification of internal stringers, and other repairs/testing techniques.
The basis for the AD is that fatigue cracking has been found in these areas. There risk is that the wing skin could potentially result in separation of the winglet and reduced controllability.
While this is a photograph of a B-737 winglet, it gives a better indication of the location.
As with many such FAA directives in the past, there are a number of comments from APB, Boeing and the US operators. They include:
- Remove a Certain Terminating Action
- Request To Add Grace Period for Post Repair (Modification) Inspections
- Request To Add Compliance Tables to Certain Service Information
- Request To Clarify Group 4 Airplanes Not Affected
- Request To Remove an Airplane Having a Certain Line Number
- Request Approval for Alternative Open Hole HFEC Inspection
- Request To Clarify Credit for Previously Accomplished Repairs Approved by an Organization Designation Authorization (ODA)
- Request To Correct Error in Service Information
Most of these involve procedural/technical questions, but deadlines and grace periods, in particular, require risk analyses. The Federal Register does not mention those calculations.
The criteria associated with airworthiness determinations are not directly at issue here. However, ADs have set technical standards in the inspection, testing, repairing and returning-to-service aspects of the mandated actions.
The certification of Part 23 has moved away from prescriptive standards and towards performance-based standards. This transition has been facilitated by the use of ASTM in setting standards, in particular to review what engineering measures should be used for innovation.
The technology of winglets is relatively new advancement. The materials and the stresses of them might benefit from the extensive, current knowledge from ASTM. In planning for the future AD processes and procedure, might it be useful to include the ASTM’s library of expertise.
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