partthe Well-examined

H ow did United save $17.6 million on engine material costs in 2005 and still maintain one of the highest

levels of reliability in the industry? The answer is Parts Manufacturing Approval (PMA) parts. But these aren’t just any PMA parts. Each one United Services approves for use on United’s aircraft has been through a strict review process, which goes above and beyond FAA requirements. They’re the same parts—and the same potential for savings—that United Services offers its other engine maintenance customers.

“We will not approve any PMA part unless in our judgment it is at least equivalent to the original equipment manufacturer (OEM) part,” says Marty O’Hagan, lead engineer–PW4000 and member of United Services’ Design Review Board.

The board—made up of experienced leaders from various specialties across the Powerplant Engineering department—serves as the final filter of an intense technical evaluation of all PMA engine parts that United Services

United Services’ strict review process means customers can choose lower-cost parts—without compromising quality.

written by

Julie Moore

photos by

Wayne Slezak

Engines

considers. “When a PMA vendor comes to us with a new part, it’s already FAA-approved. So at that point we could just put it in our engines,” says Byron May, manager–Repair, Process, and NDT Engineering and chairman of the Design Review Board. “Instead we take it through a detailed and sometimes extremely rigorous evaluation to make sure that it meets our standards.”

For customers who choose to use PMA parts, that extra level of scrutiny means they can be confident that each one will perform as well as—and sometimes better than—its OEM equivalent. It’s just one way that United Services keeps reliability high and long-term maintenance costs low.

Step by stepOnce a PMA part receives FAA approval,

its first stop at United Services is with Sandra Dahlin, business analyst for the PMA Development Team. As the person who tracks PMA parts through the evaluation process, Dahlin gathers a sample part and technical data from the PMA vendor and sends the package to the lead engineer in charge of the corresponding fleet type. The lead engineer then assigns a hardware engineer to review the part.

“The person evaluating the PMA part is the engineer who ‘owns’ that hardware at United,” says May. “He or she is responsible for that part in United’s fleet on a daily basis and keenly understands its requirements and behavior in service.”

From there, the engineer begins a compara-tive analysis, which involves comparing one or more PMA parts directly against one or more OEM parts. This evaluation can last anywhere from a few days to several months depending on how critical the part is to the aircraft’s operation. A checklist helps the engineer determine the level of criticality by placing the part in one of several categories—each with increasing levels of review, analysis, and testing. Relatively low-criticality PMA parts, such as washers or brackets, are “fast-tracked,” while parts that are deemed “signifi-cant” (such as turbine blades or fuel pump gears) receive much more comprehensive technical evaluations.

First, the engineer closely reviews technical data from the FAA and the PMA vendor to understand the FAA’s basis for approval and to ensure that the part has the appropriate instal-lation authority. Then the engineer compares

the part’s geometry to its OEM equivalent. For a fast-tracked part, this involves taking simple measurements and conducting a fit check in which the mechanic temporarily installs the part in an engine to see if it fits like the OEM part. For a significant part, the engineer takes many more measurements and compares larger populations of PMA and OEM parts. To do this, the engineer may utilize one of United Services’ coordinate measuring machines, which use a robotic arm to precisely record the part’s dimensions.

Next, the engineer focuses on the part’s material, including its chemistry, microstruc-ture, and any coatings. For more critical parts, this can involve United Services’ in-house metallurgist taking sections of both PMA and OEM parts and comparing them under optical or scanning electron microscopes.

The next level of evaluation can include a performance check, in which the engineer installs the part in the next higher assembly (such as a fuel pump) for a test bench run or in an engine for a test cell run. As an airline MRO, United Services has extensive capabili-ties—such as test benches and test cells—

Precision focus

A coordinate

measuring

machine helps

Victor Cleland

accurately record

the dimensions of a

fuel pump gear.

Minute detail

(Opposite page)

A close-up view

reveals the blades

on a PW4000 high

pressure rotor.

unitedsvcs.com • 13

Plugged in

Senna stores

component

information in the

CIDER database.

In-depth analysis

Metallurgist Aaron

Broumas loads

cross-sections of

OEM and PMA parts

into a scanning

electron microscope.

that allow the engineering team to conduct such evaluations in-house, saving the cost and time of having to turn to outside sources.

These rigorous tests are important because even minute differences between the PMA part and its OEM equivalent can influence the part’s behavior or durability in service. For some significant parts, United Services’ engineers may even perform on-site audits of the PMA vendor’s facility to ensure that quality controls of critical manufacturing processes are in place.

“It’s crucial to try and ensure that the part will perform as expected and to ensure that the 1,000th part can be as good as the first,” says May. “That’s because even a subtle difference may not cause a problem until a few years later. By then you may have a large number of parts in your fleet that are behaving in a way you don’t want.”

The final filterIf the reviewing engineer recommends that

the PMA part be approved, it goes next to the Design Review Board. The board meets every week, assessing the engineer’s evaluation of each PMA part being considered. If the part is significant, the reviewing engineer must also attend the meeting to present his or her evaluation methodology and findings.

In 2005, the board gave final approval to 205 parts. Even though they are already FAA-approved, the team rejects about 10 percent to 20 percent of PMA parts they evaluate.

For those that don’t make the cut, the rea-sons can be as seemingly minor as incorrect marking or as significant as casting disconti-nuities larger than those in OEM parts. Whatever the reason for denying approval, the team doesn’t get too specific when returning the rejected part to the PMA vendor. “We say that the part is dimensionally incorrect or materially incorrect,” says O’Hagan. “We’re very sensitive to protecting all the proprietary rights of the OEM and the PMA vendor.”

“A design drawing of a significant PMA part may have millions of dollars of engineering behind it,” says May. “So the PMA evaluation packages are handled with kid gloves and locked up at night. Even our metallurgist’s lab is locked when he steps away for a moment. We’re very strict in protecting all others’ intellectual property.”

This rigorous scrutiny means customers can rest assured that any PMA part offered by United Services is at least as good as its OEM equivalent. In some cases, the PMA part is better—providing increased reliability and peace of mind for customers. “We have exam-ples on the PW4000 where we took an OEM part that was deteriorating quite regularly on the line, and—working with a PMA vendor—we came up with an improved part, which has prevented engine removals,” says Jim Uhl, director–Powerplant Engineering and Design Review Board member.

In addition to increasing reliability and decreasing long-term maintenance costs, PMA parts can often mean further lowering of prices through competition. “What we’ve seen over the years is that after the PMA parts come out, the OEMs lower their prices to be competitive. In turn, the PMA part price could eventually go lower as well,” says Bill Kirby, engineer–Repair, Process, and NDT Engineering and Design Review Board member.

High standards

Under magnification,

cross-sections of

an OEM part (right)

and a PMA part (left)

show grain size

differences that

led to the PMA

part’s rejection

by the Design

Review Board.

14 • TAKEOFF ’06, no. 1

Collaborative effort

Byron May (right) confers with fellow Design

Review Board member, Marty O’Hagan,

on a PMA PW4000 brush seal.

Resources at workWhen it comes to engineering, United Services’

resources run deep. The staff of approximately 75 Powerplant engineers includes people like Byron May, who heads up the Repair, Process, and Non-Destructive Testing (NDT) Engineering group. With 23 years of engineering experience, May leads a team of 24 engineers in developing unique repairs to save engine, landing gear, and other parts that otherwise would have to be scrapped. The group also provides engineering support services, such as metallurgical and failure analysis, and non-destructive testing capabilities.

Since May came to United in 1989, the need for engi-neering techniques and oversights that maintain high engine reliability has become more critical than ever, especially with the increase in extended twin-engine operations (ETOPS) flights. “Manufacturers design and test an engine to validate that it’s safe and capable for that type of service,” says May. “But then it’s up to the airlines to maintain that level of safety and reliability.”

Such advances in aircraft technology are part of the reason May was drawn to aviation in the first place. Based on a lifetime love of science and “tinkering” with how things work, May transitioned from a career as an engineer with a robotic welding manufacturer to United. “I think in many ways aviation and/or aerospace is the ultimate in engineering, based on the technical complexity and achievements that have occurred in the past 40 years,” says May. “To me, jets are still cool.”

Customized serviceWith so many checks and balances to

validate their quality, it’s easy to see that PMA parts offered by United Services are a wise choice for customers. But—bottom line—it’s the customer’s choice to make. Whether they want PMA parts or OEM parts, United Services can meet their request. Combine that flexibility with United Services’ extensive repair development capabilities, and you get a level of service that’s virtually unmatched in the industry.

“If we don’t have an existing repair for a customer’s part, we can often develop one in just a few days,” says May. “If there’s no hope of developing a repair, we sometimes can offer an alternative, lower-priced PMA part that’s been scrutinized by us to a great degree. It’s just one more way we work to reduce engine material costs while maintaining high levels of engine reliability.”

Adding it upTypically, PMA parts cost 30 percent to 40 percent less than OEM parts. For United, that equals tens of millions of dollars in savings per year. Take a look at the cost savings for these five United Services-approved PMA parts.

Approved EstimatedPMA part annual savings

PW4000 seals (8 types) $2.4 millionCFM56-3 blade $1.7 millionPW2000 bearing $95,000 PW4000 EGT harness $30,000PW2000 fuel pump gears $27,000

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