https://mentourpilot.com/whats-going-on-with-boeings-787-dreamliner/

(http://www.autoadmit.com/thread.php?thread_id=5359335&forum_id=2#46451072)

The internal FAA memo relates how, early this year, Boeing reported to the FAA that Mitsubishi Heavy Industries in Japan — which builds the jet’s carbon composite wings — had discovered contamination of the composite material during fabrication that could potentially weaken the bonding when two composite parts are bonded together with adhesives.

For example, when a stiffening rod is bonded to the inside of the wing skin.

In the fabrication process for composites, carbon fiber tape impregnated with epoxy resin is laid on a mold, then hardened in a high-pressure oven called an autoclave.

Bags are placed around the composite material to create a vacuum, and a thin sheet may be placed between the composites and the mold to facilitate release when it comes out of the autoclave. The contamination occurred because some of the bagging and release materials contained polytetrafluoroethylene — commonly known by the brand name Teflon.

The use of PTFE, which left a residue after removal, did not comply with Boeing’s manufacturing specifications.

Initial tests conducted by Boeing and reported to the FAA in April showed a positive outcome: although the bond strength was reduced, it was still within the design limits.

However, the memo includes a new update from late last month, in which Boeing told the FAA that the same contamination has now been found at other major suppliers and affects not only the wing but also the fuselage and tail.

In addition, further tests of small pieces of the composites now indicated that the strength of the bond between contaminated parts in some cases was below the allowed design limits.

Boeing last month suggested to the FAA an approach to evaluating the integrity of the bonds in the affected structures. But the FAA isn’t convinced. It responded that the proposed evaluation method is not approved and not validated by testing.

https://www.seattletimes.com/business/boeing-aerospace/faa-memo-reveals-more-boeing-787-manufacturing-defects-including-contamination-of-carbon-fiber-composites/

(http://www.autoadmit.com/thread.php?thread_id=5359335&forum_id=2#46451571)

clean environments for bonding repairs on

the airplane, better ply compaction

methods to reduce porosity, drying solid

laminate, and performing heat surveys to

assure proper heat distribution during the

repair cure. Most of the repairs in the 787

SRM use tools and equipment that have

been used to repair legacy airplane

composite components and have been

available on the market for many years.

One exception is the use of a double

vacuum bag debulk (DVD) system, a newer

process that is implemented for several 787

repairs. The 787 SRM describes how

technicians can construct a DVD box from

simple lumber materials

Damage to composite structure can

manifest itself differently than in aluminum

structures. Because aluminum usually

dents or tears, damage is typically visible.

In contrast, composites will show rub

marks or a small dent. If there is enough

energy transferred, a delamination of plies

may occur. When the delamination is

critical, it will be visible on the exterior side

and/or on the interior side of the fuselage.

Because of this different manifestation of

damage, the aircraft maintenance manual

(AMM) addresses specific conditions and

inspections that need to be accomplished.

The development of the 787 also

included the creation of a simplified

inspection device to aid maintenance

personnel in assessing the extent of

damage. The inspection device, called the

ramp damage checker, was developed

specifically for the ramp technician. For

additional damage characterization and

more in-depth inspections, a wheel probe

was developed to speed and simplify the

assessment of laminate and sandwich

structures (see fig. 5). Heat damage can be

detected using instrumented inspection

Figure 5: New inspection techniques

Maintenance personnel can first use a ramp damage checker (left and center) and, if necessary, the wheel probe (right) to quickly assess the condition of

laminate and sandwich structures on the 787.

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methods as outlined in the nondestructive

inspection manual.

Please note that any significant impact

or damage needs to be inspected per the

instructions in the 787 SRM and/or the 787

AMM, chapter 5

https://skybrary.aero/sites/default/files/bookshelf/3851.pdf

(http://www.autoadmit.com/thread.php?thread_id=5359335&forum_id=2#46451596)