The Joys of Handling Aircraft Hardware
The first time I picked up a standard aircraft handbook in 1989, I was instantly amazed at the standardized aircraft hardware markings and predetermined set of part numbers that were understood by almost everyone in the aviation maintenance community. I recall studying materials and rivets in FAA Advisory Circular AC43-13, thinking that the aircraft hardware system was pretty fool proof. I could see no reason why anyone would want to alter something that had worked so well for several decades.
The reason why hardware specifications were created is fairly well understood. AN stood for “Army Navy,” and this was created so the military could have common specifications for military grade hardware, which was used by aircraft and ships alike. Naturally as WWI surplus hardware made its way into the marketplace, aviation maintenance become increasingly familiar with this concept to the extent the commercial aviation accepted these standards in its infancy. Commercial aviation became increasingly reliant on the AN standards which the military had structured. As WWII began to take shape, the United States began shipping aircraft to England (and other countries such as Russia) as part of FDR’s Lend Lease program. Before WWII, my grandfather assembled Allison V-12s in Indianapolis before he was called into the Army. These V-12s were installed in P-51 Mustangs, P-38 Lightnings, and P-40 Warhawks bound for Europe. Old timers of the Allison assembly line often shipped these engines overseas, unaware that the foreign countries receiving these aircraft had neither the tools nor spare parts familiarization to support them. As American’s became involved in supporting some British fighters such as the Hawker Hurricane and Supermarine Spitfires in the early Eagle Squadrons, aircraft mechanics from the U.S. began to scratch their heads. The British used hardware unfamiliar to the Americans, and likewise the U.S. used AN hardware that was sometimes unfamiliar to our British friends. This issue had already surfaced a few years before, and industry officials agreed something had to be done. A more public standardization needed to be identified. In 1938, the now Aerospace Industries Association began the process, which has now developed into 2800 aerospace standards. This association is the 3rd largest voluntary group of U.S. standards acknowledged by industry today. Currently, they are still tasked with monitoring and establishing industry aerospace standards that include aerospace hardware.
Sometime in the early 1990’s I started to see a profusion of changed aircraft hardware part numbers. I had grown accustomed to using AN960 series part numbers for washers, AN380 for cotter pins and AN6227 for O-rings. All of the sudden, AN960 series washers turned into a long and obnoxious NAS1149 series numbers. AN380 become MS24665 series, and AN6227 O-rings evolved in MS28775 numbers. I have always wondered what rocket scientist came up with this change, and why? It was never explained to me, so of course I had to do some research.
In the early 1990’s President Bill Clinton tasked Vice President Al Gore with overseeing a task force to help make the government more efficient. One analyst come up with the bright idea that the military should no longer support categorizing and overseeing the standards for the reportedly over 40,000 AN and MS series specifications that were used on defense contracts. The final report from Al Gore’s task force made its way to a staffer for Secretary of Defense William Perry. In what has become know in the Defense community as the “Perry Memo”, Secretary Perry stated that the Department of Defense needed to start using commercial industry parts. If a part fit over a certain dollar amount, the parts were to be built to a commercial standard. Most manufacturers were told they could no longer manufacturer under any Military specification unless a permit had been granted to do so. In a stroke of kindness, the memo stated that current contracts had 180 days until the change would be enforced, so as not to create any undue harm to suppliers. (Wow, how generous.) Since the 1990’s, you’re seeing more lubricants going to SAE standards. Many of you are surely seeing the NAS (National Aerospace Standard) and NASM (National Aerospace Standard Metric) part numbers that are making their way onto everything from bearings to bolts. This change is ongoing, and you are likely to see more of this in the future. In many cases, some items such as bearings have been given a TSO of their own, such as TSO-C149. Technical standing orders are one way that a part can be manufactured and installed as an accepted aircraft part without going thru the FAA PMA process.
When it comes to aircraft hardware, it may help you to understand how the FAA views hardware. Aircraft hardware is considered a “standard part.” We have talked about standard parts before. The FAA describes a standard part as part or material that has been manufactured to a U.S. industry or U.S. government published specification. Hardware now falls under Aerospace Industries Association, such as tires are guided by the Tire and Rim Association standards. Although the FAA does not directly regulate hardware manufacturers, they do reserve the right to oversee and monitor the use of standard fasteners in U.S. type certificated aircraft.
The term “standard part” has become muddled over the years, as some aviation maintenance operators have attempted to include commercial electronic piece parts into the category of standard parts. The FAA has been negotiating this tricky issue, as I have addressed in previous columns.
Over the years, I have facilitated the sale of more aircraft hardware than I care to admit. The one topic that every IA and A&P has asked my company about is the term “traceability.” Traceability refers to the connection between the aircraft parts that a supplier has, and where they came from. The FAA highly recommends in the “standard parts” informational letter they published, that a certificate of conformity be acquired from the producer of the material. In my experience, many hardware manufacturers will produce a pile of paperwork every time you order a large quantity of aviation grade fasteners. It has become downright impossible to provide 20 pieces of paper with every bolt that goes out the door. My recommendation, and what seems to be an industry standard, is that you insist on aircraft hardware with lot numbers on the packaging. These lot numbers, on a customer’s purchase order, should be required to automatically print off on any certificate of conformance that your parts distributor will provide you. If this were something new that you have not heard of, I would have a discussion with your supplier. Sometimes, Chance Aviation will buy a large quantity of hardware for a certain customer requirement. Since we digitally scan all of our FAA 8130-3s and manufacturer receiving reports, we have learned to also keep permanent digital copies of manufacturers certificate of conformance documents. We have seen in several situations, that electronic (digital) copies of such paperwork facilitate a reduction in workload latter. Many hours can be wasted trying to prove traceability in an audit.
The aerospace fastener industry really policies itself well. Several years ago, the US Department of Commerce instituted a commercial fastener quality program called the Fastener Quality Act. Although it has been revised since 1990, the act provides quality guidance for fastener manufactures. The act was signed into law, however the Department of Commerce exempted aerospace fasteners, as they are under the administration oversight of the FAA. This act encompassed a wide range of industry standards including mandatory laboratory testing, and industry accreditation. The reason for this commercial standardization is that several foreign imported hardware items were passed off to the Department of Defense as a high quality SAE Class 8 bolts. A number of high profile hardware failures (non-aviation) promoted the U.S. Defense Industrial Supply Center to conduct an audit of industrial fasteners in 1990. The results of that study were that over 40% of all inbound commercial hardware failed to meet quality standards. The new fastener act required commercial hardware manufacturers to use some of the same processes that aircraft hardware manufacturers had used for decades, particularly in marking their hardware and testing for quality compliance. Should you have concerns that the hardware you have does not meet the quality standards you are aware of, by all means set it aside. I would recommend that you read the FAA Advisory Circular AC21-29B on detecting and reporting suspected unapproved parts. Aircraft hardware is covered in this AC, and some good points are made.
As always, I have some parting advice on saving money with aircraft hardware purchases. Over the years, I have noticed that many manufacturers are issuing newer parts catalogs that no longer list alternate AN/MS hardware part numbers for everything from wheel bolts to exhaust nuts and bearings. Keep your older parts catalogs, as you may well have that OEM bearing in stock under the older MS number. We have spent a lot of time entering cross-reference AN/MS part numbers in stock for items that are common. Trust me, there is no sense paying three times for a bolt when you can get the standard hardware version for a more reasonable price.
Norman Chance is president and CEO of Chance Aviation, an international aircraft parts distributor headquartered in Indianapolis. He has a degree in aircraft maintenance from Vincennes University and a degree in aeronautics from Embry-Riddle University. He holds an FAA A&P certificate