Boeing is reassuring airlines over the use of composite material for the primary structure of the 787 following claims by Airbus that the new Boeing twinjet could be grounded “because of a scratch in the paint”.
The claims, made at a recent safety conference in the USA, refer to Boeing’s decision to certificate the 787 for inspections for visible damage only without the need for non-destructive tests and represent “misinformation from the other side”, says 787 chief mechanic Justin Hale. “We all know composites can hide damage and so right up front we decided we’d certify for visible damage only,” he says.
Boeing says the basic design criterion for the 787 is founded on two key properties of the solid laminate composite; the non-propagation of cracks from undetected damage; and the inherent capability of the composite material to maintain structural integrity – even with small amounts of undetected damage.
The result, says the company, is that small areas of damage are acceptable for the life of the aircraft because they will never grow into a bigger, and potentially dangerous structural issue. “We have to demonstrate we’re good for these sorts of damage to the ultimate load for the life of the aircraft. That’s why it makes me cringe when I hear them say undetected external damage could result in catastrophic failure, because there is so much margin being built into the structure,” says Hale.
“We’ve always tried to keep safety out of the discussions between Airbus and ourselves. We think Airbus builds a pretty safe aircraft, and it was pretty startling for us to hear Airbus roll out in a safety conference that accelerated damage is the biggest hurdle we have to overcome.” Hale adds that even though a series of bonded repair methods have been developed, and will be available to the airlines, “in general all of the repairs will most likely be bolted. Airlines may decide in the heavy check to pull off the bolted repair and clean it up with a bonded repair at that point.”
In the meantime, the airlines appear to be expressing concern over the issues raised by Airbus. “We’ve put a request to our development group for more chunks of (composite) barrel to counter what appears to be misinformation from the other side,” he says.
Airbus stresses the advantages of aluminium lithium for the fuselage skin panels of the A350 in terms of resistance to accidental damage, and its ability to undergo standard repair procedures.
GUY NORRIS/LOS ANGELES
Source: Flight International
