Safety Message

1
May 19, 05
Safety Message 1
All aspects of composite maintenance and repair
are interlinked
1) The damage to a composite aircraft component
must be first discovered (if discovered
by operations personnel, it must be reported to
maintenance) 2) The damage must be assessed by
qualified maintenance personnel 3) Damage
disposition must include an interface with
engineering personnel familiar with
approved data for the structure in question 4) If
repair is necessary, the repair design must be
approved by the appropriate authority
(previously approved data such as may be
documented in a SRM or other approved
repair method) 5) The chosen repair method must
also be of an approved type (previously
approved data such as may be documented in a SRM
or FAA DER) 6) The approved repair process must
be performed by a qualified technician, using
qualified materials, and strictly adhering to
the appropriate in-process controls 7) The
completed repair must be inspected for approval
by a qualified inspector
If any of the above maintenance actions contain
errors or flaws, then a deficient repair may
result. It is essential for safety that
qualified inspectors, technicians and engineers
are involved in composite maintenance and repair.
2
May 19, 05
Safety Message 2
Composite aircraft structural components can be
damaged by many different sources. In many cases
these components are designed to withstand
damages up to levels within the bounds of
performance and cost. When damages are
above these levels and approved data exists for
repair, source documentation (e.g., SRM) will
typically provide the necessary instructions for
maintenance actions. This will include the
appropriate NDI methods to accurately map the
extent of the damage and an approved repair that
can be performed to allow the aircraft to be
returned to service. If the damage is of a level
not covered by previously approved data that has
been documented and made available, then the
original equipment manufacturer (OEM) must be
contacted for repair disposition or an FAA DER
will be needed to develop a repair design and
generate the data needed to substantiate the
repair.
Damage disposition and subsequent repair designs
and processes must be based on approved data,
which substantiates the structural integrity.
Without such data, the airworthiness of the
structure is in question.
3
May 19, 05
Safety Message 3
The approved sources of technical data,
maintenance and repair instructions, guidelines
and regulatory requirements contain information
vital to proper aircraft maintenance and repair.
It is essential to be familiar with the specific
aircraft structure drawing system and approved
maintenance methods for the particular component
in question. The use of inappropriate or
unapproved maintenance instructions for a given
part, including inspection and repair processes
or alternate repair materials used on other
structures, is not allowed. While it is not
included in the roles of inspectors and
technicians to be fully cognizant with the FARs,
ACs and ADs, it is appropriate that all members
of the repair team be aware that these regulatory
requirements exist and are understood by at least
one person in the repair process.
Any lack of understanding of the structural
detail, or deviation from the approved data,
maintenance and repair instructions or regulatory
requirements can lead to unacceptable maintenance
procedures and a defective repair.
4
May 19, 05
Safety Message 4
The correct processing of composite components is
critical to the elimination of processing
defects. This includes all steps in processing,
such as surface preparation, material handling
and storage, material lay-down, part bagging and
cure, and post-process inspection. Inspection of
bonded composite and metal-bond assemblies using
appropriate NDI techniques together with
in-process quality control is essential to the
delivery of defect free composite components for
assembly to the aircraft. Equally, adherence to
the correct repair processing steps, in-process
quality controls and post-process inspection is
crucial to successful composite repairs. In
addition to the above steps for the original part
fabrication, composite repair procedures will
require damage removal, and acceptable surface
preparation for bonding. Note that these
procedures may also include drying. The
particular fabrication and repair methods for a
given structural part will often include specific
processing details that are unique to that part.
In the event of processing mistakes, misuse of
equipment, or misinterpretation of in-process
quality controls and post-process NDI results
composite part fabrication or repairs may be
compromised. Parts delivered with unaddressed
defects, and compromised repairs may not be
airworthy.
5
May 19, 05
Safety Message 5
In-service inspections of composite components
are necessary for safe flight operations just as
they are for those components fabricated from
metals. In-service damages to composite parts
from various sources are likely to occur during
an aircrafts operational life. Per maintenance
instructions, damages may be detected using
visual inspection or by directed NDI. Visual
indications of outside surface damage should be
followed up with a backside inspection if
accessible. If damage is first detected using
visual methods, NDI techniques such as pulse echo
or even a simple tap hammer will generally be
needed to determine the full extent of the damage
and make the correct disposition. The correct
use and interpretation of NDI are required to
accurately define the extent of damages so that
correct damage dispositions can be made.
In the event of in-service damages, it is crucial
for safe flight operations that these damages are
discovered, either by operations personnel, or
directed maintenance inspections, before they
become critical. After damage has been
discovered, the correct damage disposition must
be made in order that the damage can, either be
determined to be acceptable, or the damaged
component can be repaired and the aircraft
returned to safe flight operations.
6
May 19, 05
Safety Message 6
As in the fabrication of composite bond
assemblies, correct processing is critical to the
elimination of defects in bonded composite
repairs. Bonded repairs are more difficult to
inspect for structural integrity than bolted
repairs. As a result, correct procedures in
surface preparation, moisture elimination, proper
material storage and handling, and in-process
controls are essential for defect free bond-lines
and patches. A poorly bonded repair may be more
detrimental to flight safety than the original
damage, due to the potential for repair
separation during flight. This relates to a need
to remove all damaged material before applying a
bonded repair. If the bonded patch is not
effective or separates in service, the resulting
damage size is larger and more critical than the
original damage. A repair that separates in
flight can cause damage to other components. If
a repair to a flight critical component does not
completely separate, it could cause flutter of
that component and other components to which it
is attached.
Strict adherence to repair bond process
procedures and in-process quality controls are
vital for flight safety as well as to prevent the
need for costly re-works. Current post-repair
NDI methods are necessary but not sufficient
proof of a good bond.
7
May 19, 05
Safety Message 7
Defects may be present in the bond line or within
the repair patch due to poor surface preparation,
material storage and handling and cure process
mistakes. It is essential to use the appropriate
inspection methods for specific types of bonded
repair (i.e. sandwich, laminate stiffened or
metal-bond components). Post-repair inspection
should be visual followed by an appropriate NDI
technique. Visual inspection can be, in some
cases, just as valuable as NDI methods such as
pulse-echo for detecting flawed bonded repairs.
Similar to the message in Safety Message 4 for
damage detection and disposition, misuse of
equipment during post-repair inspections, or
misinterpretation of inspection results may be
detrimental to safety.
8
May 19, 05
Safety Message 8
In general, there will be differences in the
machining and fastening steps needed to complete
a bolted repair of composite structure. Specific
differences in bolted repairs should also be
expected for different composite structures. The
tolerances for installation of fasteners during
composite bolted repairs are, in many cases, more
critical than for installation of fasteners
during the repair of metal parts. Drilling of
composites is more difficult than drilling
metals, and fasteners need to be selected so that
they do not cause delamination during
installation. Details of the bolted repair
design are also of great importance. A repair
design that is not substantiated by approved data
may cause problems for component margins of
safety, while repairing the damaged area
adequately. Fastener installation equipment such
as torque wrenches etc. must be correctly
calibrated and standards kept up to date.
The design of the bolted repair, selection of
incorrect fasteners, poorly drilled holes and
incorrect fastener installation can all
contribute to a defective or unapproved repair,
and hence flight safety may be impaired.
9
May 19, 05
Safety Message 9
As in Safety Message 1, all aspects of composite
repair are interlinked and teamwork is essential
to provide a safe damage and/or repair
disposition. It is essential that each member of
the team recognizes his/her limitation to a)
disposition a damage, b) determine the repair
design and process that have been substantiated
by approved data, c) perform the approved repair,
and d) inspect and approve the completed repair.
If any of the above repair aspects contain errors
or flaws, then the aircraft may be dispatched
with a deficient or unapproved repair.