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There is now physical proof that the fan blades should have an earlier retirement life.
The rate is not low enough to live with, since this catastrophic failure was entirely preventable if new fan blades had been installed on the engine.
Did the 2016 incident of uncontained engine failure in a Southwest plane of a very similar age have the same problem?
Ln #537, N766SW; 18.0 years; 27 Aug 2016 date of incident , uncontained engine failure (returned to active service)
Ln #601, N772SW; 17.8 years; 17 Apr 2018 date of incident, uncontained engine failure (in storage during investigation)
Quote:
Originally Posted by lvmensch
But the rate is low enough to live with. It might also be good to note that SW has been cancelling some flights to get engines inspected. Probably running down and checking all the ones with high cycles on them.
One of the first planes they suspended from flying for one day was N766SW, the plane involved in a similar incident in 2016
Did the 2016 incident of uncontained engine failure in a Southwest plane of a very similar age have the same problem?
Ln #537, N766SW; 18.0 years; 27 Aug 2016 date of incident , uncontained engine failure (returned to active service)
Ln #601, N772SW; 17.8 years; 17 Apr 2018 date of incident, uncontained engine failure (in storage during investigation)
One of the first planes they suspended from flying for one day was N766SW, the plane involved in a similar incident in 2016
That is not the age of the turbine blades. They are swapped out on a different cycle.
Did the 2016 incident of uncontained engine failure in a Southwest plane of a very similar age have the same problem?
Ln #537, N766SW; 18.0 years; 27 Aug 2016 date of incident , uncontained engine failure (returned to active service)
Ln #601, N772SW; 17.8 years; 17 Apr 2018 date of incident, uncontained engine failure (in storage during investigation)
One of the first planes they suspended from flying for one day was N766SW, the plane involved in a similar incident in 2016
"One fan blade separated from the fan disk during the accident flight and
The root of the separated fan blade remained in the fan hub; however, the remainder of the blade was not recovered."
I do not know how many flight hours, or more importantly, how many cycles of loading, the fan blades had accumulated in each of the two failed engines. Clearly in both incidents, the fan blades should have been swapped out sooner. The FAA and GE did not fix the problem after the first failure, so now we had a second failure.
I do not know how many flight hours, or more importantly, how many cycles of loading, the fan blades had accumulated in each of the two failed engines. Clearly in both incidents, the fan blades should have been swapped out sooner. The FAA and GE did not fix the problem after the first failure, so now we had a second failure.
Wikipedia only lists three incidents, but it is not clear if that was meant to be a comprehensive list. Is it reasonable to guess that both Southwest engines still had original fan blades?
One issue that led to accidents with the CFM56-3C engine was the failure of fan blades. This mode of failure led to the Kegworth air disaster in 1989, which killed 47 people and injured 74 more. After the fan blade failed, the pilots mistakenly shut down the wrong engine, resulting in the damaged engine failing completely when powered up for the final approach. Following the Kegworth accident, CFM56 engines fitted to a Dan-Air 737-400 and a British Midland 737-400 suffered fan blade failures under similar conditions; neither incident resulted in a crash or injuries. After the second incident, the 737-400 fleet was grounded.
At the time it was not mandatory to flight test new variants of existing engines, and certification testing failed to reveal vibration modes that the fan experienced during the regularly performed power climbs at high altitude. Analysis revealed that the fan was being subjected to high-cycle fatigue stresses worse than expected and also more severe than tested for certification; these higher stresses caused the blade to fracture. Less than a month after grounding, the fleet was allowed to resume operations once the fan blades and fan disc were replaced and the electronic engine controls were modified to reduce maximum engine thrust to 22,000 lbf (98 kN) from 23,500 lbf (105 kN). The redesigned fan blades were installed on all CFM56-3C1 and CFM56-3B2 engines, including over 1,800 engines that had already been delivered to customers.
In August 2016 Southwest Airlines Flight 3472 suffered a fan blade failure, but landed later without further incident. While the aircraft sustained substantial damage, there were no injuries.
On April 17, 2018, Southwest Airlines Flight 1380 suffered from what appears to be a fan blade failure, debris from which punctured a window. The Boeing 737-700 landed safely, but one passenger was killed and several were injured.
The life of the Life Limited Parts is complicated. Virtually all are removed before 30,000 Engine Flight Cycles...but some depending on thrust and other variables may be as low as 7500 engine flight cycles.
So you have to get into the specifics of the engine and its usage to determine what the life of an LLP is.
Wikipedia only lists three incidents, but it is not clear if that was meant to be a comprehensive list. Is it reasonable to guess that both Southwest engines still had original fan blades?
The fan blades may have been replaced on those engines at some point in time, but whatever blades were installed, had been used for too long. Otherwise they would not have suffered a low cycle fatigue failure (assuming this is LCF as the high cycle fatigue failures had been corrected).
The projected life of the blades should have been adequately shortened after the first failure. Having two failures gives GE/Safran data to project the actual life of the currently designed blades. GE and Safran need to improve their "lifing" methodology for fan blades. Other GE engines do not have this problem, I think the fan is the responsibility of Safran.
Hopefully GE/Safran are successfully sued over this.
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