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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.

Flight Fleets Analyzer shows that the aircraft was built in 1999, and has been operated by Qantas since new.

After receiving advice from Boeing, the cracked strut ribs were removed and sent to the manufacturer for further specialist examination. Meanwhile, the 747 was repaired and returned to service after completing its shop visit, the Australian Transport Safety Bureau says.

The examination confirmed that five cracks were present in the strut ribs, which were consistent with fatigue cracking. Further analysis concluded that they were likely due to the vibration loading on the pylon consistent with normal operations of the engine.

The ATSB concluded that the extent of the cracking did not affect the structural integrity of the pylon, and thus safety was not compromised.

It also noted that Qantas’s maintenance programme had decreased the interval at which the 747s engine pylons are inspected to 24 months, as opposed to Boeing’s recommendation of 48 months.

“The reduced inspection interval proved effective in this case, detecting cracks before they reached a level considered by the manufacturer to be a safety risk.”

The ATSB adds that the occurrence highlights the importance of vigilance during routine maintenance activities, while it also encouraged operators to review their maintenance schedules, particularly for ageing aircraft.

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