ASN Wikibase Occurrence # 190870
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| Date: | Sunday 26 December 1999 |
| Time: | 10:10 |
| Type: |  Boeing 747-238B |
| Owner/operator: | Qantas |
| Registration: | VH-ECB |
| MSN: | 21977/409 |
| Year of manufacture: | 1979 |
| Fatalities: | Fatalities: 0 / Occupants: |
| Aircraft damage: | Minor |
| Category: | Incident |
| Location: | 33 km N Brisbane Airport -
 Australia
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Brisbane International Airport, QLD (BNE/YBBN) |
| Cairns, QLD | |
| Investigating agency: | ATSB |
| Confidence Rating: |  Information verified through data from accident investigation authorities |
While climbing through approximately 10,000 ft after take off, the crew of the Boeing 747-238, VH-ECB, heard an audible bang and felt a jolt through the airframe. The number 1 engine parameters were observed to fluctuate momentarily and the indicated Engine Pressure Ratio dropped by about .15 to 1.35. All other engine parameters remained normal and the aircraft remained free of vibration and control asymmetry. A visual engine inspection by the crew revealed nothing abnormal. After consulting with ground engineers in Brisbane, the crew decided to continue to Cairns. An inspection at Cairns revealed that most of the engine's cold stream nozzle was missing, a number of the outboard leading edge flap panels were damaged and the outboard flap canoe was holed.
The investigation determined that cracking and delamination of the acoustic lining skin at the top right side of the nozzle had been reported during the transit inspection at Cairns on 22 December 1999. An Engineering Authority had been issued to allow the aircraft to proceed after minor repairs to the acoustic liner were effected. The thrust reverser had also been locked out as a precaution and the aircraft then operated nine sectors before the nozzle failed.
The operator advised that delamination of the acoustic liner is a known defect. However, investigation determined that the cracking had originated in the nozzle structure adjacent to the acoustic liner. There is no requirement for inspection of this area during service. The area cannot be inspected in-situ without the removal of panels and the use of a visual aid.
A fleetwide check by the operator found a further six nozzles cracked in the same area. The nozzles were replaced before further flight. A detailed inspection of the removed nozzles determined that the cracking had originated at the top rivet hole of the standoff which supports the outer skin of the nozzle. The cracks varied in length from about 2 cm to 21 cm. The incident thrust reverser assembly, of which the nozzle formed part, had accumulated 19,621 hours since the last heavy maintenance inspection and 56,716 hours since new. The only inspection requirement is a visual inspection of the thrust reverser assembly at approximately 15,000 hours or shop visit when this area of the nozzle is visible. However, the nozzle assembly can be swapped between engines depending on the operators requirements. As the units are not serialised it is difficult to determine each nozzles time in service.
The manufacturer's recommended inspection requirements failed to detect cracking of the cold stream nozzle structure which resulted in failure of the nozzle.
Sources:
https://www.atsb.gov.au/publications/investigation_reports/1999/aair/aair199906038
Revision history:
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