Victoria Moores MadridViews diverge on bonded repairs
to primary composite structures
T
here is still some way to go before bonded repairs will be
accepted on primary composite structures, according
to executives speaking at Aviation Week’s MRO Europe
Conference.
Regulators only allow bolt-on metal repairs to primary
composite structures on the latest generation of aircraft—
just like standard metallic-build versions—because of con-
cerns over the strength, quality and durability of manually
bonded repairs.
“There is still the debate between bonded and bolted re-
pairs. We need both,” says James Kornberg, AFI KLM E&M
aerostructures product and business development general
manager.
While Lufthansa Technik is working with Airbus and other
industry stakeholders to automate and standardize bonded
composite repairs as part of the Composite Adaptable In-
spection and Repair (CAIRE) project team (see sidebar),
Kornberg is unconvinced. “It is very interesting, but practi-
cally this system cannot be used because it is not validated.
Today we don’t think it is necessary to have a robot to repair
these aircraft,” he says.
Kornberg argues that in the fi eld it is too tricky to get theproper tooling for bonded repairs and recreate the conditions
needed, so bolted repairs will continue to take the lead. “You
cannot do bonded repair on very large areas. It is technically
not possible, so there is a limit. It is case-by-case. You have
the right to push for bonded repairs, but it will not always
be possible.”
Bombardier’s director of engineering & component ser-
vices Michael Curran agrees. “We’re doing a huge amount
of work on bonded repairs. For instance, if something needs
fi xing during the manufacturing process it’s not going to be
done with a bolted repair. But we have the advantage of clean
rooms, autoclaves and perfect vacuums. The dif culty is re-
producing that in the fi eld,” he says.
Both agreed that the prime objective is getting the air-
craft back into service as quickly as possible, with a mini-
mum cost for repairs, adding that bonded repairs lend
themselves more to secondary structures such as nacelles
and fan cowlings.
“You don’t want to touch it again. That works with bolted
repairs. There is no limit to how many bolt-on repairs you
could do,” says Curran. The metal fi x, which carries a weight
and strength penalty, will then fl y with the aircraft until the
end of its life, or until the structure is replaced. Curran de-
scribed this as “fi t and forget.”
Bombardier is establishing bolt-on repair procedures for
the CSeries, testing potential events such as heat exposure
and lightning strikes. “The big message to take out of this is
we’re not going to be doing carbon-type repairs. These are
metallic repairs that bolt onto the structure, which should
make it easier for MROs and airlines. It is not necessary at
this point to do carbon repairs everywhere,” he says. cBolt-on Repairs
MRO Edition COMPOSITES
AviationWeek.com/mro AVIATION WEEK & SPACE TECHNOLOGY MRO EDITION NOVEMBER 3/10, 2014 MRO31B
olt-on metal repairs to primary composite structures could
become a thing of the past, as work to improve the accep-
tance and standardization of bonded repairs progresses.
Bolted repairs can be detrimental, cutting the composite
structure’s residual strength by up to 50% and adding extra
weight. “We have made the fi rst step—not in convincing the
authorities—but in increasing the reliability and acceptance of
bonding as a repair method,” says Christian Sauer, Lufthansa
Technik engineering manager for airframe-related component
services, speaking at Aviation Week’s MRO Europe Conference.
“The only [primary structure] repair that is certifi able at
the moment [for visible damage] is bolted, meaning that just
like a standard metallic aircraft you put a bolted patch on it.
The problem is [that] bonding—which we believe is the best
way to repair composite aircraft—is not allowed by the regula-
tors,” he says.
This is because bonded repairs are largely done manually and
it is hard to prove the strength, quality and durability of the joint
without breaking it again. There is also a lack of specialized train-
ing for bonding, fueling regulators’ concerns, says Sauer.
“The quality of the repair depends on the skill of the me-
chanic. There is no system that can tell you how much it canwithstand. All of these uncertainties mean the authorities
don’t allow us to do this on primary structures,” adds Sauer.
“What we need to do is take all uncertainties out of the pro-
cess. We need an industry standard for bonding, which has
started; but we are not there yet.”
Using technologies from the CAIRE project, Lufthansa Tech-
nik and its partners have developed an automated system for
assessing, designing and repairing damage to composite struc-
tures. It optimizes the repair before scanning the surface for
contaminants, grinding out the damaged material and creating
the fi x, which is applied manually. Afterwards, the new geometry
can be checked to ensure all the dimensions have been met.
CAIRE also has been adapted from a stationary in-shop sys-
tem to a mobile robot that can be secured to any surface using
suckers. “You can move it where you want, and it can do this pro-
cess wherever it is needed,” says Sauer.
This “very precise, very quick” automated process could
replace the current system of manual layer-by-layer grinding to
create a bonded fi x, which lacks standardization and is extremely
time-intensive—taking at least 60% longer than the automated
process. Tests on the automatically produced repairs have proven
they are 5-15% stronger than the manually ground alternative. cCAIRE ABOUT COMPOSITES
圀漀爀氀搀䴀愀最猀⸀渀攀琀圀漀爀氀搀䴀愀最猀⸀渀攀琀
圀漀爀氀搀䴀愀最猀⸀渀攀琀