Exact Replica: Inspection Efficiency

From simple bushings to critical engine components, producing replacement aircraft parts requires unwavering commitment.

The “spare parts” market for aircraft is anything but spare. Airlines that once purchased parts to maintain their aircraft and engines almost exclusively from OEMs such as Boeing and GE Aviation now have the option of buying from third-party manufacturers approved by the Federal Aviation Administration. It’s a fast-growing market for shops that can meet strict FAA regulations regarding the design, manufacture and QC of the parts.

OEMs hold FAA “type certificates” authorizing production of complete aircraft or engines. The FAA also has “parts manufacturer approval” (PMA) rules for other suppliers wishing to make replacement parts for aircraft and engines.

Courtesy of HEICO Parts Group

At the HEICO Parts Group, a 5-axis laser finishes the complex geometry of a T56 Hastelloy X jet-engine combustion chamber component.

PMA regulations cover two areas: approval of the part design and definition of the QC systems governing part production. The design process usually begins with reverse engineering, or what the FAA calls “test and computation of the original part.”

Federal part-replacement standards initiated after World War II were generally applied to simple parts for legacy aircraft. As economic pressures on air carriers grew, interest in PMA parts for more sophisticated applications increased. In 2009, the FAA clarified regulations to make it clear that PMA parts and OEM parts are held to the same quality standards. Today, PMA parts are authorized for critical parts, including engine components.

Images courtesy of PMA Products

PMA Products Quality Inspector Jeremy Kimrey performs receiving inspections on 6.325 “-long, 0.624 “-dia. landing-gear bolts (below) made from aerospace-grade alloy steel.

The main advantage of PMA parts is they can cost 20 to 50 percent less than OEM parts. As a result, interest in PMA parts is growing. At the Modification and Replacement Parts Association (MARPA) annual conference in October, consulting firm ICF SH&E, Cambridge, Mass., estimated that the global PMA market will grow from $410 million in 2011 to $750 million by 2018, with engine parts being the largest category.

Learn from Experience

One PMA focus includes components for general aviation. Causey Aviation Service Inc., Liberty, N.C., provides general and charter aviation management, maintenance and avionics sales. Experience gained from years of aircraft maintenance and parts replacement led the owners to form PMA Products Inc., a PMA replacement parts company also based in Liberty.

“We reverse engineer a lot of simple parts, such as bolts, bushings and landing-gear parts,” said Charles Causey, president of PMA Products. Although simple, the parts are thoroughly analyzed. “For example, if it is a steel part, we send it to a lab and have the material analyzed to determine what alloy is used,” Causey said. “If it is plated, we determine what type of plating it has. Hardness is always checked and heat treatment must be a consideration. Then we have to establish the dimensions of the part and a range of tolerances on the dimensions.” Part design details are documented and reported to the FAA.

Courtesy of Jet Parts Engineering

Jet Parts Engineering provides PMA components for airlines and independent MROs worldwide.

Causey said most of the parts the company produces are for aircraft from Piper Aircraft Inc. and Hawker Beechcraft Corp. Causey Aviation previously was a Piper sales and service center and operated Piper aircraft, and so is familiar with typically replaced parts.

When the company began to operate Beechcraft King Air planes, it was shocked by replacement part prices. “We came up on a 5-year landing-gear overhaul and were just floored by the price of some of the bolts and bushings,” Causey said. “We were already doing PMA parts for Piper aircraft, so we decided to PMA some of the Beechcraft parts. Now we are selling a lot of the Beechcraft parts to landing-gear overhaul shops.” While OEMs continue to supply parts at higher prices, Causey noted that OEMs have reduced some of their prices.

PMA Products subcontracts parts manufacturing after designing the parts and obtaining the approvals. The FAA oversees design and production. “They have to approve our QC systems and inspect them on a regular basis,” Causey said. “For parts considered critical by the FAA, we are required to go into our subcontractors’ facilities and inspect them.”

Word of mouth sometimes determines the choice of a subcontract shop. “We talk to other people in the PMA business that are having similar parts made and learn about shops they have confidence in,” Causey said.

Branching Out

Because airlines and aerospace OEMs operate globally, there is global interest in PMA parts. Jeff Dark, vice president of sales and marketing for Jet Parts Engineering Inc., Seattle, said its customers are major airlines, including Delta, Lufthansa and United, as well as independent airline repair stations worldwide.

Many PMA companies, Dark said, focus on one area of the aircraft or aircraft systems. Jet Parts Engineering, for example, is mostly involved in the component and accessories field, which includes hydraulics, pneumatics, flight controls and fuel systems. “We recently purchased the assets of an engine hardware company, so we are into that now as well. As the market is maturing, PMA companies are branching out to find opportunities where they can.”

The company first produced PMA parts for Boeing airframes, then moved into supplying parts for regional aircraft makers and Airbus. Except for some assembly, Jet Parts Engineering subcontracts its manufacturing work.

Courtesy of Star Novak, McFarlane Aviation

McFarlane Aviation President Dave McFarlane (right) and Machine Shop Supervisor Brad Price at the shop’s dual-head, CNC MultiCam router where 2024T3 Alclad aluminum control surface skins are being vacuum fixtured for trim-out.

A number of factors influence the choice of parts to replicate. “We get a lot of usage downloads from different airlines and maintenance and repair organization (MRO) shops,” Dark said. “That lets us vet parts ourselves through our database. And customer requests are a major driver. When one feels an OEM part is too expensive, we will look at it.” If the customer is a big airline, its usage alone can justify a project. Jet Parts Engineering holds 570 PMAs, with a goal of adding 120 each year.

In addition to providing lower-cost replacement parts, PMA companies may redesign parts to improve performance. “We have made some minor improvements to parts that affected their life,” Dark said. “If you make a change like that, you have to explain your reasoning to the FAA and get it approved.” For example, an upgrade might involve changes in the way a gear fits on a shaft, with the intent of minimizing the likelihood of rubbing that could accelerate wear.

Dark said the company’s choice of reverse-engineering methods for a part depends on the application and critical dimensions. Most of the reverse-engineering processes, including measurement and metallurgical analysis, take place in-house. However, he said, “Our engineers may choose to outsource the reverse engineering on some parts with a high level of geometric complexity or special material features.”

Responsive service is a key element of the PMA business. Almost all of Jet Parts Engineering’s parts are in stock and can be shipped within 24 hours, compared to typical lead times of 2 to 12 weeks for OEMs, according to Dark.

In-House Production

In contrast to PMA providers that subcontract most manufacturing, McFarlane Aviation Inc., Baldwin City, Kan., designs and manufactures many PMA parts. Most of the PMA parts McFarlane manufactures are for general aviation, although the company is also a Tier 2 or Tier 3 supplier for Boeing, Airbus and the U.S. military. The shop’s specialty is components that require swaging (metal reduction) to fabricate assemblies, such as push-pull controls for throttles and auxiliary control systems.

Dave McFarlane, president, said the company generally chooses parts for PMA that can be improved. “Many times we use more modern materials; we try to bring the technology up to more recent standards,” he said. “Some of the parts we replace were designed 60 years ago. Our biggest driver is customers who are dissatisfied with original part life. Of course, price plays into it too.”

Courtesy of HEICO Parts Group

PMA parts undergo processing identical to their OEM counterparts. This automated shot peen equipment at HEICO Parts Group creates a compressive residual layer to increase fatigue resistance in jet engine components.

To improve a part, McFarlane determines its failure mode. A good example of relatively simple but flight-critical products are seat rails for light aircraft, machined from heat-treated 2024 aluminum alloy extrusions. The rails are subject to cyclical loading as the pilot’s weight moves in rough air, McFarlane said. “They’ve had trouble with the seat slipping because of hole wear and cracking in the rail.” In a worst-case scenario, a shifting seat could cause a pilot to lose control of the aircraft.