Home' Asian Aviation : AAV June 2014 Contents 24 AsianAviation | JUNE 2014
wrong-footed by its American counterpart. The
787’s promise of greater fuel efficiency and lower
maintenance costs had charmed the market,
resulting in a lukewarm reception for the A350.
After going back to the drawing board, Airbus
came up with the A350 XWB. This revised model
incorporated 53% composites, albeit with a more
cautious panel – rather than barrel – fuselage
Having stolen a march on Airbus, Boeing knew
MRO workshops would be tasked with validating
its ambitious claims. The fire-damaged Ethiopian
787 presented by far the biggest challenge to date,
and the manufacturer could ill-afford any further
“That was one of the largest composite primary
structure repairs ever done,” Hoke recalls. “There
had been quite a few successful repairs to 787
structures already, but this one at Heathrow was far
and away the biggest. It was an important repair to
get done correctly.”
The Ethiopian aircraft had suffered major heat
damage to the crown of the fuselage near the
intersection of aft Section 47 and the tail unit.
Boeing’s use of barrels meant that a replacement
skin patch would have to be glued onto the scorched
area of the fuselage, which was in a difficult-to-reach
location on top of the aircraft.
Nonetheless, Hoke says it was a “pretty
straightforward” repair that Boeing had been fully
prepared to handle. “It wasn’t terribly difficult to do
the repair once they had decided on the design,” he
insists. “The time-consuming part was not physically
doing the repair. It was getting agreement from all the
insurance companies and the regulatory authorities
and everybody that was involved on how to do it. That
took months and months.”
Scaffolding was erected at Heathrow, and a team
of Boeing specialists arrived in the UK to do the
delicate job last autumn. It would ultimately take just
a few days to complete.
Boeing remains tight-lipped about the precise
repair work, but The Seattle Times quoted sources
within the company as saying a composite skin
patch had been cut out from another barrel on
its 787 production line. A corresponding hole
with rounded edges was then removed from the
damaged area of the Ethiopian jet, and the skin
patch was dropped into place.
Small gaps around the patch were reportedly
plugged with a paintable sealant designed to
expand and contract as the fuselage pressurises
and depressurises during flight. Inside the aircraft, a
splice plate was glued between the original skin and
the patch, and the adhesive cured by heat blankets
held under pressure by vacuum bags. The patch
was also mechanically fastened to the surrounding
frames and stringers.
The work therefore used both bonded and bolted
repairs to fully restore structural integrity, enabling
Ethiopian to resume flying the aircraft in December.
For Boeing, the successful repair job was a vital
riposte to critics who had questioned its fuselage
design. Few observers ever doubted the viability of
bolted repairs – whereby technicians mechanically
fasten doublers onto damaged areas – as the
process closely resembles repair work on metallic
aircraft. But the complexity of bonded repairs had
been a concern.
Yet despite Boeing’s success, two questions
remains. First, what certification standards will be
adopted to re-train technicians in this relatively
unfamiliar field? And second, is the added headache
of repairing composites compatible with Boeing’s
promise of lower maintenance costs?
Rather than independently setting the standards for
training and certifying composite repair technicians,
the FAA is allowing the industry to establish its own
That is in keeping with how the FAA has
historically licenced aircraft-certified welders and
Non-Destructive Inspection (NDI) technicians. FAA
advisories effectively delegate responsibility to
bodies such as the American Welding Society or
the American Society for Nondestructive Testing.
In the case of composites, SAE International
is leading the charge to establish technical
standards and certifications via its Commercial
Aircraft Composite Repair Committee (CACRC).
It envisages four different levels of training, with
technicians being assessed by auditing division the
Performance Review Institute.
“It’s close to being implemented,” confirms Hoke,
who is himself a member of CACRC. “They’ve been
working on this for years and years.”
Jan Popp, chairman of CACRC and project
manager of new technologies and innovation at
Lufthansa Technik, agrees that comprehensive
training is required for employees across the sector.
He notes that the first step towards repairing an
aircraft is taken by ground staff, who must visually
identify damage from the tarmac. Only then can
impact energies be calculated and the Structural
Repair Manual (SRM) consulted.
“One of the main challenges is training not only
the guys in the back-shop, but also the maintenance
personnel who have daily contact with those aircraft,”
Popp explains. “As soon as he sees something from
the outside, then he has to call maintenance and they
will check the SRM to see if the visible damage is
within the allowable damage limit. If not, they have
to use NDI testing to decide what kind of repair is
The impact of a lightening strike on composite material without any protective material whatsoever, from a test carried out by Dexmet. Ken Burtt, vice
president of sales and marketing at Dexmet, says: “Damage to unprotected composite surfaces from a lightning strike would include melting of the resin
at high temperatures, resulting in severe damage to the surfaces and potentially a rupture of the skin.” Some form of lightening protection for composite
material on aircraft is standard practice.
“There had been quite a few
successful repairs to 787 structures
already, but this one at Heathrow was
far and away the biggest. It was an
important repair to get done correctly.”
President, Abaris Training Resources
29/05/2014 8:15:17 PM
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