United B777 engine failure
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Sixty (60) days after the last publicly stated projection of when these aircraft could be expected to return to scheduled service (see a few posts above), today's Wall Street Journal publishes an article describing the projected return as occurring early next year, rather than the timing this summer previously hoped-for by United.
Article relates that Pratt & Whitney is continuing work on blade inspection methods (reportedly, ultrasound) and that Boeing is working on modification of the engine cover. Not new information itself, IIRC.
United executive quoted as noting certain constraints on system flight ops imposed by continuing unavailability of these aircraft.
Article relates that Pratt & Whitney is continuing work on blade inspection methods (reportedly, ultrasound) and that Boeing is working on modification of the engine cover. Not new information itself, IIRC.
United executive quoted as noting certain constraints on system flight ops imposed by continuing unavailability of these aircraft.
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Several major news outlets reporting FAA has issued a statement directing changes to PW4000 powerplants on United's 777s, aimed at strengthening the covers [correction: cowlings]. Also directing inspections. As described in this reporting, these directions are aligned with previously announced FAA guidance or updates.
Boeing, Pratt & Whitney, and United each issued statements (reportedly) generally signaling concurrence with FAA's directives. (Not located any of the actual statements yet.)
Boeing, Pratt & Whitney, and United each issued statements (reportedly) generally signaling concurrence with FAA's directives. (Not located any of the actual statements yet.)
Last edited by WillowRun 6-3; 23rd Dec 2021 at 13:33.
"The proposed directives would require: strengthening engine cowlings, enhanced engine fan-blade inspections and inspections of other systems and components, [and] specific corrective actions depending on the inspection results"
FAA proposes modifications and inspections of Boeing 777 engines
Nothing surprising here. It's a big no-no that the engine nacelle fell apart after a fan blade out event - that's not supposed to happen (and it's long been recognized as a safety of flight concern). I'm sure Boeing has been working on a design change for the PW4000/112" nacelle (especially after it happened a second time - indicating the first one wasn't some sort of fluke). But Boeing can't mandate that operators incorporate the retrofit - only the regulators can do that.
Similarly, two FBO events on the PW4000/112" (in a fairly short period of time) was pretty damning evidence that the existing inspection requirements were inadequate and needed to be changed. Again, Pratt can recommend the change, but you need the feds to mandate it.
Similarly, two FBO events on the PW4000/112" (in a fairly short period of time) was pretty damning evidence that the existing inspection requirements were inadequate and needed to be changed. Again, Pratt can recommend the change, but you need the feds to mandate it.
The National Transportation Safety Board determines the probable cause(s) of this incident to be:
The fatigue failure of the right engine fan blade. Contributing to the fan blade failure was the inadequate inspection of the blades, which failed to identify low-level indications of cracking, and the insufficient frequency of the manufacturer’s inspection intervals, which permitted the low-level crack indications to propagate undetected and ultimately resulted in the fatigue failure. Contributing to the severity of the engine damage following the fan blade failure was the design and testing of the engine inlet, which failed to ensure that the inlet could adequately dissipate the energy of, and therefore limit further damage from, an in-flight fan blade out event. Contributing to the severity of the engine fire was the failure of the “K” flange following the fan blade out, which allowed hot ignition gases to enter the nacelle and imparted damage to several components that fed flammable fluids to the nacelle, which allowed the fire to propagate past the undercowl area and into the thrust reversers, where it could not be extinguished.
NTSB Final Report for UAL 328 / N772UA
The fatigue failure of the right engine fan blade. Contributing to the fan blade failure was the inadequate inspection of the blades, which failed to identify low-level indications of cracking, and the insufficient frequency of the manufacturer’s inspection intervals, which permitted the low-level crack indications to propagate undetected and ultimately resulted in the fatigue failure. Contributing to the severity of the engine damage following the fan blade failure was the design and testing of the engine inlet, which failed to ensure that the inlet could adequately dissipate the energy of, and therefore limit further damage from, an in-flight fan blade out event. Contributing to the severity of the engine fire was the failure of the “K” flange following the fan blade out, which allowed hot ignition gases to enter the nacelle and imparted damage to several components that fed flammable fluids to the nacelle, which allowed the fire to propagate past the undercowl area and into the thrust reversers, where it could not be extinguished.
NTSB Final Report for UAL 328 / N772UA
The National Transportation Safety Board determines the probable cause(s) of this incident to be:
The fatigue failure of the right engine fan blade. Contributing to the fan blade failure was the inadequate inspection of the blades, which failed to identify low-level indications of cracking, and the insufficient frequency of the manufacturer’s inspection intervals, which permitted the low-level crack indications to propagate undetected and ultimately resulted in the fatigue failure. Contributing to the severity of the engine damage following the fan blade failure was the design and testing of the engine inlet, which failed to ensure that the inlet could adequately dissipate the energy of, and therefore limit further damage from, an in-flight fan blade out event. Contributing to the severity of the engine fire was the failure of the “K” flange following the fan blade out, which allowed hot ignition gases to enter the nacelle and imparted damage to several components that fed flammable fluids to the nacelle, which allowed the fire to propagate past the undercowl area and into the thrust reversers, where it could not be extinguished.
NTSB Final Report for UAL 328 / N772UA
The fatigue failure of the right engine fan blade. Contributing to the fan blade failure was the inadequate inspection of the blades, which failed to identify low-level indications of cracking, and the insufficient frequency of the manufacturer’s inspection intervals, which permitted the low-level crack indications to propagate undetected and ultimately resulted in the fatigue failure. Contributing to the severity of the engine damage following the fan blade failure was the design and testing of the engine inlet, which failed to ensure that the inlet could adequately dissipate the energy of, and therefore limit further damage from, an in-flight fan blade out event. Contributing to the severity of the engine fire was the failure of the “K” flange following the fan blade out, which allowed hot ignition gases to enter the nacelle and imparted damage to several components that fed flammable fluids to the nacelle, which allowed the fire to propagate past the undercowl area and into the thrust reversers, where it could not be extinguished.
NTSB Final Report for UAL 328 / N772UA
Simulation studies indicated that the carbon fiber reinforced plastic (CFRP) honeycomb structure of the event engine inlet and inlet aft bulkhead was unable to dissipate and redistribute the energy of the loads imposed by the (Fan Blade Off) event in the same manner as the aluminum structure inlet that was used during certification tests.
How can such a thing happen? Was the FAA aware of the design change or was it signed off by a Boeing "FAA Representative"?
I found this rather significant
This reads to me that the fundamental design of an element that is subject to certification testing was changed, but the new design was not subjected to certification testing.
How can such a thing happen? Was the FAA aware of the design change or was it signed off by a Boeing "FAA Representative"?
This reads to me that the fundamental design of an element that is subject to certification testing was changed, but the new design was not subjected to certification testing.
How can such a thing happen? Was the FAA aware of the design change or was it signed off by a Boeing "FAA Representative"?
That being said, there definitely would have been testing done on the new CFRP nacelle components in order to certify the change. However, they are NOT going to do a full-blown repeat of the fan blade out test - such a test is terrifically expensive (at least $50 million) to demonstrate a nacelle material change. Rather, testing and analysis would have been performed to show that the new CFRP could handle the same loads as were measured in the original FBO tests. However FBO test are highly dynamic and the loads that are measured may or may not be fully representative of what the structure will actually see, and the associated analyses are something of an art rather than an exact science. Apparently in this case they got it wrong.
