1. Engines
the Well-examined
part
written by
Julie Moore
photos by
Wayne Slezak
United Services’
strict review process
means customers
can choose lower-
cost parts—without
compromising quality.
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

2. 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 step
Once 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 the part’s geometry to its OEM equivalent. Precision focus
United,” says May. “He or she is responsible For a fast-tracked part, this involves taking A coordinate
for that part in United’s fleet on a daily basis simple measurements and conducting a fit measuring
and keenly understands its requirements check in which the mechanic temporarily machine helps
and behavior in service.” installs the part in an engine to see if it fits Victor Cleland
From there, the engineer begins a compara- like the OEM part. For a significant part, accurately record
tive analysis, which involves comparing one the engineer takes many more measurements the dimensions of a
or more PMA parts directly against one or and compares larger populations of PMA fuel pump gear.
more OEM parts. This evaluation can last and OEM parts. To do this, the engineer may
anywhere from a few days to several months utilize one of United Services’ coordinate
depending on how critical the part is to the measuring machines, which use a robotic
aircraft’s operation. A checklist helps the arm to precisely record the part’s dimensions.
engineer determine the level of criticality by Next, the engineer focuses on the part’s
placing the part in one of several categories— material, including its chemistry, microstruc-
each with increasing levels of review, analysis, ture, and any coatings. For more critical parts,
and testing. Relatively low-criticality PMA this can involve United Services’ in-house
parts, such as washers or brackets, are “fast- metallurgist taking sections of both PMA
tracked,” while parts that are deemed “signifi- and OEM parts and comparing them under
cant” (such as turbine blades or fuel pump optical or scanning electron microscopes.
gears) receive much more comprehensive The next level of evaluation can include a
technical evaluations. performance check, in which the engineer Minute detail
First, the engineer closely reviews technical installs the part in the next higher assembly (Opposite page)
data from the FAA and the PMA vendor to (such as a fuel pump) for a test bench run or A close-up view
understand the FAA’s basis for approval and to in an engine for a test cell run. As an airline reveals the blades
ensure that the part has the appropriate instal- MRO, United Services has extensive capabili- on a PW4000 high
lation authority. Then the engineer compares ties—such as test benches and test cells— pressure rotor.
unitedsvcs.com • 13

3. 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
In-depth analysis that allow the engineering team to conduct equivalent. In some cases, the PMA part is
Metallurgist Aaron such evaluations in-house, saving the cost better—providing increased reliability and
Broumas loads and time of having to turn to outside sources. peace of mind for customers. “We have exam-
cross-sections of These rigorous tests are important because ples on the PW4000 where we took an OEM
OEM and PMA parts even minute differences between the PMA part that was deteriorating quite regularly on
into a scanning part and its OEM equivalent can influence the line, and—working with a PMA vendor—
electron microscope. the part’s behavior or durability in service. we came up with an improved part, which has
For some significant parts, United Services’ prevented engine removals,” says Jim Uhl,
engineers may even perform on-site audits director–Powerplant Engineering and Design
Plugged in of the PMA vendor’s facility to ensure that Review Board member.
Senna stores quality controls of critical manufacturing
component
High standards processes are in place.
information in the
Under magnification, “It’s crucial to try and ensure that the part
cross-sections of
CIDER database. will perform as expected and to ensure that
an OEM part (right) the 1,000th part can be as good as the first,”
and a PMA part (left) says May. “That’s because even a subtle
show grain size difference may not cause a problem until
differences that a few years later. By then you may have a
led to the PMA large number of parts in your fleet that are
part’s rejection behaving in a way you don’t want.”
by the Design In addition to increasing reliability and
Review Board. The final filter decreasing long-term maintenance costs, PMA
If the reviewing engineer recommends that parts can often mean further lowering of prices
the PMA part be approved, it goes next to the through competition. “What we’ve seen over
Design Review Board. The board meets every the years is that after the PMA parts come out,
week, assessing the engineer’s evaluation of the OEMs lower their prices to be competitive.
each PMA part being considered. If the part In turn, the PMA part price could eventually
is significant, the reviewing engineer must go lower as well,” says Bill Kirby, engineer–
also attend the meeting to present his or Repair, Process, and NDT Engineering and
her evaluation methodology and findings. Design Review Board member.
14 • TAKEOFF ’06, no. 1

4. Customized service
With so many checks and balances to Adding it up
validate their quality, it’s easy to see that
PMA parts offered by United Services are Typically, PMA parts cost 30 percent to 40
a wise choice for customers. But—bottom percent less than OEM parts. For United, that
line—it’s the customer’s choice to make.
Whether they want PMA parts or OEM parts,
equals tens of millions of dollars in savings per
United Services can meet their request. year. Take a look at the cost savings for these
Combine that flexibility with United Services’ five United Services-approved PMA parts.
extensive repair development capabilities,
and you get a level of service that’s virtually
unmatched in the industry. Approved Estimated
“If we don’t have an existing repair for a PMA part annual savings
customer’s part, we can often develop one in
just a few days,” says May. “If there’s no hope PW4000 seals (8 types) $2.4 million
of developing a repair, we sometimes can offer CFM56-3 blade $1.7 million
an alternative, lower-priced PMA part that’s
been scrutinized by us to a great degree. It’s PW2000 bearing $95,000
just one more way we work to reduce engine PW4000 EGT harness $30,000
material costs while maintaining high levels PW2000 fuel pump gears $27,000
of engine reliability.”
Resources at work
When 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
Collaborative effort engineer with a robotic welding manufacturer to United.
Byron May (right) confers with fellow Design “I think in many ways aviation and/or aerospace is
Review Board member, Marty O’Hagan, the ultimate in engineering, based on the technical
on a PMA PW4000 brush seal. complexity and achievements that have occurred in the
past 40 years,” says May. “To me, jets are still cool.”
unitedsvcs.com • 15