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
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.