Certification aircraft are placed in sophisticated jigs which simulate wing loading, airframe stress and a variety of loads.  These dedicated airframes fly thousands of hours in these jigs allowing designers to detect stress fractures long before the actual aircraft experiences and problems.  In this particular case the wing is latterly bent upward or downward to simulate a load 1.5 times greater than the design limit.  Unfortunately, the wing failed a 1.45 times or approximately 3 per cent shy of the certification requirement.

Airbus spokeswoman Barbara Kracht said the wing will need some "refinements" but the aircraft is on schedule for certification and first deliveries late this year. "We will need to find out from the data what is really needed but it's certainly not a redesign of the wing," Kracht told Associated Press.