Originally posted bt tdracer
Breaking a turbine blade is not a big deal - high vibes and a probable engine shutdown, but unlikely to threaten continued safe flight and landing
May be with airline equipment
td but certainly not the case with all turbines.
Analysis of two failures I've had with Turbomeca products. In both cases all the blades on the disc had been trashed. Operator had four similar failures that I'm aware of. Following lifted from the safety authority report.
Occurrence report 200100584
On 7 February 2001, a Sikorsky S76C helicopter belonging to the same operator, with two crew and ten passengers on-board, was in a hover with the flight crew completing before take-off checklist items. The pilot reported that while trimming the engines, a "pop" was heard. He then noted that the left engine turbine gas temperature (measured at point T4 within the engine) was in excess of 1000 degrees C. The helicopter was then landed uneventfully. The flight crew reported that the only cockpit indication of imminent failure was the almost simultaneous illumination of the left engine chip (magnetic particle) detector advisory.
Examination of the helicopter revealed minor shrapnel damage to the left engine exhaust extension and engine cowling. There was no reported engine fire. The left engine was removed and sent to the engine manufacturer for disassembly and examination. The manufacturer's final report noted a separation of turbine blade number six of the GG second stage disc. The blade was separated above the 'fir tree' attachment point but below the blade platform, and had punctured the second stage nozzle guide vane turbine ring. One adjacent blade (number seven) in the direction of turbine wheel rotation was also noted as cracked.
Metallurgical examination by the manufacturer attributed the blade failure to a low-cycle fatigue cracking mechanism. The manufacturer concluded that abnormal loading was the major contributing factor in the failure, given the reported absence of anomalous material features or evidence of high-temperature operation. Dimensional inspections failed to reveal any sign of non-conformity that could have led to the development of the abnormal loads. However, the manufacturer stated that turbine blade platform/GG disc interferences were also a potential factor that could have aggravated the fatigue failure of the blade.
At the time of the occurrence, Arriel 1S1 engine, serial number 15522, had accumulated 4,737.4 hours and 4,471 cycles since new. It had accumulated 1,740.0 hours TSO and 1,615 cycles since overhaul. Following overhaul, the engine was installed on March 11, 1999. Module three did not have turbine blade plasma coating modification TU204 incorporated.
Occurrence report 199602839
On 9 September 1996, a Sikorsky S76C helicopter belonging to the same operator, experienced an in-flight engine failure of the right engine while taking off from an oil platform. A loud noise was heard before the engine failure. (My note, there was no noise prior to the failure, the failure occurred with a massive explosion, akin to a grenade exploding - have experience with those as well) The right engine was shut down and the crew completed an uneventful single engine return to the Longford base. There was no reported associated engine fire. The right engine was removed and sent to the manufacturer for disassembly examination.
At the time of the occurrence, Arriel 1S1 engine serial number 15513, had accumulated 2,282.0 hours and 1,949 cycles since new. The manufacturer provided the operator with a final report noting the rupture (separation) of one GG turbine blade with subsequent rear bearing damage and GG seizure. Their report stated that the separation was suspected to be the result of blade rubbing with the second stage nozzle guide vanes with no signs of fatigue or abnormal over temperature operation. Module three had turbine blade plasma coating modification TU204 incorporated.