The FAA has released new advisory guidance that applies to quality assurance systems for forged rotating components made from nickel alloys. This guidance will apply to manufacturers producing parts like disks, spacers, hubs, shafts, spools and impellers.
Federal Aviation Regulation 33.15(b) requires that:
“the suitability and durability of materials used in the engine must … [c]onform to approved specifications (such as industry or military specifications) that ensure their having the strength and other properties assumed in the design data.“
To achieve this goal, the FAA expects manufacturers to rely on certain inspection and oversight practices that meet the FAA’s interpretation of current industry best practices. The oversight is designed to confirm that the materials conform to the properties assumed in the design data.
The FAA explains that current industry best practices for inspection anticipate that the frequency and size of the anomalies tolerated in the rotating component design and lifing analysis will be less than might have previously been permitted (in other words, they are going to tighten the standards without changing the rules).
AC 33.15-2 provides guidance on how to establish manufacturing processes and inspections (in-process material and component inspections as well as finished component inspections), for the manufacture of premium quality, nickel-base, alloy-forged rotating components, such as disks, spacers, hubs, shafts, spools and impellers (but not blades).
There is significant text in this AC devoted to the melt process used for the nickel. The AC anticipates that the PMA holder will exercise control over the metal supplier, and will jointly develop oversight protocols with the smelter. Remember, the new quality assurance procedures that apply to PMA holders and applicants require supplier control mechanisms. 14 C.F.R. 21.137.
The AC explains that production approval holders should ensure that their suppliers have effective process controls, particularly with respect to melting and remelting metals. The production approval holder should work with the metals supplier to develop and document significant process control points, parameters, and control limits. The production approval holder must establish a method to document and approve changes to the process control documents.
Unfortunately, our informal inquiry among manufacturers suggests that many PMA manufacturers are purchasing their metals by specification number and then testing the materials using sampling techniques. They do not typically get involved in direct quality assurance oversight of smelters to ensure that they are smelting correctly. This appears to create a disconnect between the current standard practices and the FAA’s new guidance.
MARPA Board Member Dennis Piotrowski explained to me:
“I have been to several forging houses, metal suppliers, and smelters. Quite honestly, even if a company (OEM/PMA) had a person stationed 100% of the time, the individual would not see everything going on. There simply is no substitute for the end item user (OEM/PMA) to do some sort of risk assessment and based upon the results, establish appropriate inspection requirements, imposed at appropriate stages of manufacturing, e.g.: certified lab reports, independent lab reports, coupons submitted with the lot, destructive inspection, etc.”
If you are manufacturing nickel alloy rotating engine parts, then please be sure to read the new advisory circular and let us know whether you think (1) this will affect your business and (2) it provides reasonable guidance for oversight of metal suppliers.