Aircraft Engines: A Need for Increased Performance and Safety

Turbine engine of airplaneThe necessity for a robust aircraft engine design is strongly associated with not only flight performance, but also to passengers’ safety. The fatigue on the blade of CFM56 engine did not prove to be fatal in last August’s incident. None of the 99 passengers was hurt, but parts of the engine broke apart damaging the fuselage, wing and tail, and forcing the Boeing Co. 737-700 to an emergency landing. However, that was not the case in July 6, 1996, when the left power plant on a Boeing MD-88 broke apart while accelerating for take-off and the shrapnel was propelled into the fuselage killing a mother and a child seated in the Delta Air Lines Inc. aircraft [1]. A few years earlier, in January 8, 1989, a CFM56-3 blade failure proved to be fatal for 47 out of 118 passengers of the British Midlands Airways (BMA) Ltd Flight 92 departed from London Heathrow Airport en route to Belfast International Airport. Based on Federal Aviation Administration’s accident overview [2] post-accident investigation determined that the fan blade failed due to an aero-elastic vibratory instability caused by a coupled torsional-flexural transient non-synchronous oscillation which occurs under particular operating conditions. An animation describing this process is available at the following link: (Fan Blade Failure).

The last example [3] of this not so cheerful post took place on July 29, 2006, when a plane chartered for skydiving experienced jet engine failure and crashed. Tragically, there were no survivors. The failure was attributed to aftermarket replacement parts. The aircraft was originally equipped with Pratt & Whitney jet engines, specifically made with pack-aluminide coated turbine blades to prevent oxidation of the base metal. However, during the plane’s lifetime, the turbine blades were replaced with different blades that had a different coating and base metal. As a result of the replaced turbine blade not meeting specification, it corroded, cracked and caused engine failure.

As it can be observed, there are several reason why an engine can fail varying from inspection mistakes, manufacturing processes and design strategies. Nowadays, engine failures are far below the leading causes of accidents and death. Nevertheless, they are ranked fourth in the decade from 2006 through 2015 with 165 fatalities, according to Boeing statistics [4]. When it comes to blade fatigue regular inspections and maintenance play the most important role. However, the design process is equally important to ensure an efficient and powerful design. The design of the machine under specific flight conditions, taking into account aero-structure interaction, as well as vibration and Rotor dynamics analysis is essential to get a streamlined solution. AxSTREAM allows the user to investigate a variety of design points and further analyse the best solution that meets the constraints and operating conditions requirements. Moreover, AxSTREAM NET can now be used to estimate leakages and cooling or bleed air flow parameters for different fluid path sections while taking into account heat exchange of cooling flow with metal surfaces.

References:

[1] https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR9801.pdf

[2] http://lessonslearned.faa.gov/ll_main.cfm?TabID=2&LLID=62&LLTypeID=2#null

[3] http://www.robsonforensic.com/articles/aircraft-engine-materials-expert

[4] http://www.dallasnews.com/business/airlines/2016/09/12/investigators-cracked-engine-blade-broke-southwest-airlines-flight-last-month

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