The Boeing 747-436 aircraft, G-BNLD, departed Sydney, Australia, at 17:29 hours. Approximately one hour into the flight, while the aircraft was in cruise at flight level 330 (FL330), the crew experienced the sudden onset of heavy airframe vibration and received an ENG 3 REVERSER annunciation from the engine indicating and crew alerting system (EICAS). The crew initially reduced the no.3 engine power and carried out the ‘Engine Reverser Unlocked’ actions from the aircraft quick-reference handbook (QRH). The crew stated that the engine appeared to be functioning normally at that time. After further EICAS status and advisory messages however, the crew elected to carry out other QRH checklists, concluding with the shutdown of the no. 3 engine. The captain made a PAN call to air traffic control and subsequently an advisory announcement to the passengers. To reduce airframe vibration after the engine was shut down, the first officer, who was the handling pilot, descended the aircraft to FL180 and reduced airspeed. A third crew member who was resting at the time of the event went back into the cabin to examine the engines and found extensive damage to the no. 3 engine nacelle and strut fairings. After that information was reported to the flight crew, a further QRH checklist Fire Engine, Severe Damage or Separation was actioned, although at no time was there any reported indication or sign of fire. A decision to return to Sydney was made and fuel was jettisoned to establish a landing weight within limits. In consideration of the damage to the engine and to minimise the risk should the engine or components separate, an over-water approach to runway 34L was requested. The aircraft landed safely at 19:47. Significant Factors: 1. During the 1991 manufacture of the first-stage low-pressure compressor blade serial number GB77535, a small area of incomplete bonding remained within the interface between the two titanium alloy plates used to fabricate the blade component. 2. The presence of the incompletely bonded region was detected during preliminary non-destructive inspection, however the blade was accepted for service under the manufacturer’s ‘concessional assessment’ program. 3. The maximum acceptable bond-line defect size limits as specified by the concessional assessment program were too large to ensure that fatigue cracks could not initiate and propagate to failure within the prescribed life limit of the blade components. 4. None of the manufacturer’s prescribed periodic in-service inspections carried out on the blade during its life had detected the incomplete bond defect. None of these inspections were specifically designed for the detection of defects within the lower aerofoil section where the defect was located. 5. Fatigue cracking initiated and propagated from the upper edge of the bond-line defect in response to service loading conditions. 6. Fracture and release of the fan aerofoil section from the rotor occurred after growth of the cracking to critical size. 7. The number-3 engine failed from damage sustained during the blade failure event. 8. The aircraft sustained minor airframe and number-4 engine damage resulting from impacts with blade debris liberated from the number-3 engine nacelle and cowling.