While climbing through 1,500 ft after take-off from Hobart, the crew of the Boeing 737 advised air traffic services that the number one engine had failed and was being shut down. The crew returned the aircraft to Hobart. There was no evidence of fire.
Disassembly and inspection of the CFM56-3C1 engine, serial number 856135, traced the failure to the loss of a 15 x 20 mm segment of trailing edge from a single high-pressure turbine blade. The passage of the segment through the turbine resulted in extensive damage to all four stages of the low-pressure turbine assembly, rendering the engine inoperative. The subject blade was subsequently removed and examined by the Australian Transport Safety Bureau.
The failed blade, serial number 849M8, had accumulated 26,576 hours and 17,928 cycles since new. Maintenance records indicated that the blade received a "full" repair in the manufacturer's facilities in Singapore in June 1997 and was subsequently installed into the subject engine where it accumulated 10,226 hours and 5,332 cycles. The repair involved the use of Rene 80 alloy. The blade also received a "mini tip" repair in July 1995. On that occasion Inconel 625 alloy was used.
The reason for the "full" and "mini tip" repairs was to rebuild the blade tip area eroded due to the high operating temperatures and pressures. Any thermal cracks in the area were checked and removed at that stage. The "full" and the "mini tip" repairs were carried out in approved repair facilities in accordance with the appropriate manufacturer's repair documents. There was no difference between the repairs as far as the extent of the blade weld repair, materials and techniques used. The only difference was in the area of the blade coating.
The subject blade and the high-pressure turbine were periodically inspected in accordance with the manufacturer's and operator's maintenance programs. Those programs required the high-pressure turbine to be inspected at intervals not exceeding 1,140 hours. The inspection required detailed examination of the convex and concave mid-chord tip areas for radial cracks and of the blade trailing edge for axial cracks. The procedure specified the permissible crack length and imposed engine service limitations if cracks exceeded the limits.
The subject blade had accumulated 660 hours since it was last inspected on 11 August 2000. Following that inspection the high-pressure turbine was certified as serviceable.
The operator advised of a similar failure to a high-pressure turbine blade from another CFM56-3 engine. That item showed the loss of a similar section from the blade trailing tip corner but without the catastrophic consequences for the rest of the turbine and the engine.
The engine manufacturer indicated that that type of blade failure was not new. Although not every blade failure was reported by the engine operators, the manufacturer received reports of a number of similar cases each year. The manufacturer indicated that no formal records of the failed blades, their time in service, and repairs, were maintained.
