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Closer inspection interval detected cracking on 747 pylon
Qantas’s decision to halve the time between inspections on the engine pylons of its Boeing 747-400 fleet allowed it to detect fatigue cracking before it became a safety issue. The affected 747, registered VH-OJT, was undergoing maintenance in Hong Kong on 5 October 2016 when an inspection of the number two engine pylon identified cracks that had started to develop in the outboard strut ribs in the torque box of the pylon. (www.flightglobal.com) 更多...
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Well done Qantas by setting a good example!
Curious as to how any level of "cracking" can be considered acceptable. In the world of welding inspection any crack detected by any inspection method is rejected.
ASME allows linear indications up to 1/16" before they become relevant and/or rejectable in most instances. AWS does not allow.
ASME B31.1, "Power Piping" states that cracks - external surface are unacceptable without a length for visual examination. It's also the same for Radiography and Ultrasonic examination.
Some of the parts on the aircraft are very difficult to get to and only can be inspected with the airplane out of service for several days. These inspections are scheduled regularly (several hundred hours/flights, typically).
Basic fracture mechanics/damage tolerance assumes that there IS a flaw in the aircraft at critical locations, and predicts how fast those flaws will grow during flight cycles. When a crack is found, it is repaired if it is a fracture critical part. For less critical parts, it is sometimes adequate to stop drill the crack and delay the repair until the plane is out of service, so there are situations where it is possible to live with a known crack.
Basic fracture mechanics/damage tolerance assumes that there IS a flaw in the aircraft at critical locations, and predicts how fast those flaws will grow during flight cycles. When a crack is found, it is repaired if it is a fracture critical part. For less critical parts, it is sometimes adequate to stop drill the crack and delay the repair until the plane is out of service, so there are situations where it is possible to live with a known crack.
Hopefully others will take notice and do the same as Quantas.
