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FAA Grounds Certain 777-200s Following Incident in Denver

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Following yesterday's incident, where a United Airlines Boeing 777 suffered an engine failure after departure from Honolulu, the FAA declared that all Boeing 777s equipped with Pratt & Whitney PW4070 engines would be grounded until further notice. This would allow for a more thorough investigation in the matter whilst ensuring the safety of passengers on these aircraft. (theexplorerblog.com) さらに...

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mbrews
mbrews 4
The article is helpful. It narrows the concern to the specific PW models under scrutiny, namely those with 112 inch diameter fan. Not sure whether the EAD will cover all submodels, which range from 77,000 LBS thrust to 98,000 LBS thrust.

As stated elsewhere, concern is about the ones with hollow blades
ColinSeftel
Colin Seftel 4
The PW4000 series engine is used on many other aircraft: B747-400, B767, KC-46, MD-11, A300, A310 & A330. Why is the FAA only grounding B777s?
nasdisco
Chris B 11
The 777 version of the engine has a unique blade design not shared with other variants of the engine.
FrankHarvey
Frank Harvey 0
What is/are the advantage(s) of hollow blades over solid blades ?

It seems to me that solid blades would be far more robust, easier to manufacture and visibly inspect than hollow blades. A solid blade with the same exterior dimensions as a hollow blade is more substantial. In a hollow blade a surface defect such as a crack might form on the inside void and thus not be detectable without sonic equipment but a similar surface defect would be visible on the exterior of a solid blade.
ffrcobra1
ffrcobra1 6
Weight. The hollow blades weigh over 30 pounds each. Heavier solid blades would put added stress on the root area of the blade and the blade attach area of the hub, which would then require those areas to be reinforced, which equals even more weight. Even solid blade can develop subsurface cracks which are not visually detectable.
FrankHarvey
Frank Harvey 3
Thanks. Reducing weight (Torsten Hoff said "mass", the same thing) seems to make a lot of sense especially to reduce the centrifugal force on the hub attachment. I hadn't realised the blades weighed as much as 30 lbs each.

Looking at the photographs it appeared that either a leading fan blade or an initial compressor stage blade had broken.

I initially thought the hollow blade was for cooling, and I could understand that for later stages where air was heated under compression or, more especially, for the turbine blades. But for the fan, or initial compressor blades, cooling didn't make sense to me. I felt that at the initial stages the airflow over the blades would be at ambient temperature and even after the air had passed the initial compression stages I can't imagine there would be so much of a heat increase as to require special cooling of the blade internals.

I could also imagine channels being designed in such a way as to induce uniform heat expansion of the blade material thus maintain the same blade profile. But again this would be more applicable to the later stages, especially the turbines.

So thanks both Torsten and Ffrcobra1 for taking the time to explain, I can well understand Mass/Weight reduction.
328thBS
Eric Dillinger 3
Actually, weight and mass are not the same. Mass is the same regardless of gravity. Weight is the product of mass multiplied by the acceleration due to gravity.
ffrcobra1
ffrcobra1 2
I believe there was a guy who postulated that mass multiplied by acceleration equals force.
ffrcobra1
ffrcobra1 3
Glad I had knowledge that was actually useful. That doesn’t happen often.
There has been mention of previous blade problems on this model engine. It is amazing that the pics of the front of the engine from the 2018 incident in Hawaii are almost indistinguishable from the pics of the plane in DEN yesterday. Here’s a link to the report and pics of the 2018 event. It’s like deja vu all over again.
https://data.ntsb.gov/Docket/?NTSBNumber=DCA18IA092
TorstenHoff
Torsten Hoff 8
Some turbine blades are hollow to provide cooling passages and to reduce mass. The blades need to periodically be inspected non-visually anyway, so there is little disadvantage compared to solid blades.
FrankHarvey
Frank Harvey 1
Thanks for the reply.
mbrews
mbrews 3
As mentioned by Chris B, and as reported elsewhere, the P&W models of concern are PW4000-112 with 112 inch blades. There are 7 sub-models of thrust rating.

That said, many recent engine failures occurred with specific engine model PW 4077, 77,000 LBS thrust and basically the oldest units of the PW4000-112 series.
jptq63
jptq63 1
Noting the age / these are the older / oldest units, do you think P&W / FAA / Boeing may use the data to extrapolate and maybe re-rate newer (as well as these engines) for expected life / Time Between Major Overhaul for the engines? If so, it starts to make me wonder about operating costs, etc..., and how the airlines pick an engine for their fleets. I am guessing given the directive to ground and inspect, there maybe a significant change coming and wonder if this would also apply to the other engine manufactures and engine designs; clarification, hollow vs. sold blade designs.
mbrews
mbrews 2
You raise some good questions about inspection intervals and life. I really dont know about such impacts. There will be laser hot focus on NDT methods for this engine type, because of the similar 2018 blade loss incident with reg. N773UA .

And big time focus on the complete loss of inlet ring and cowling.

If you spend a lot of time around CYYZ, you probably won't need to duck for falling engine parts :) Air Canada's remaining 777-200 series are GE-90 powered. They have been parked since November 2020
ColinSeftel
Colin Seftel 2
Flight Global reports that the UK has now also grounded PW4000-112 engines.
https://www.flightglobal.com/safety/uk-bans-operations-with-pw4000-powered-777s/142548.article
rds24a
Richard Sucher 2
I read turbofan engine designs are required to take extensive measures to prevent uncontained engine failure, particularly those from a predictable scenario such as a blade failure. The tests I've seen online for blade-out situations are all done on static test stands at ground level. The temperature and pressure conditions at flight speeds and altitudes, however, would be much different than in a static test stand. My guess is that newer models can accomplish more realistic testing via simulation, but older models didn't benefit from such analysis.
Quirkyfrog
Robert Cowling 1
Simulating an engine failure, if you mean on a computer, concern me. Nothing can 'simulate' reality except reality.

Case in point, the video I saw this morning said that 'investigators were surprised to see a huge gash in the area of the wing root structure on the plane'. An engine failure isn't unheard of, but it can cause massive damage to the wing, and, as we know already from the SouthWest incident, damage to the passenger cabin as well. If part, or all of, the severed parts had gone through the wing, this Denver incident would have had a completely different, and horrific, conclusion. It wouldn't be engine parts raining down, but flaming wreckage and bodies.

'Simulating' potential catastrophic conditions, again if that is what you are suggesting, shouldn't even be considered.

Perhaps forbidding the use of hollow blades, or the use of multipart fan assemblies, and more often performing deep inspections of fan assemblies is what is needed. The engine is a complex garbage disposal that is not meant to swallow pieces of itself. If a bypass fan blade was sucked into the later stages, and that is what caused the failure, which it appears to be the case, then a rework of the design seems in order. As those fans get larger, there is a heck of a lot of force applied to those blades. Nothing is going to stop a blade, or blades, from ripping through the engine cowling/nacelle and anything else in its path. Same as propeller driven plane, only instead of one blade, you have potentially dozens, and with a higher level of momentum.
mbrews
mbrews 1
Well, you're raising some good points. As a poster stated below, photos of the 2018 engine damage are almost indistinguishable from the recent incident. What else do they have in common ? Wait for it ... Complete loss of cowling.

Among other things, discharge of a fire bottle becomes ineffective. Mostly like a "white fart into the wind" as I heard in a pilot's utube video

There's speculation elsewhere about the materials of construction in a bulkhead.
Possibly a newer composite material differs from an aluminum material used on the engines for certification in say 1993 or 1994.
Mokey
BRETT JACOB 1
I always loved the sound on the original United 777s. Shame they’ll be leaving soon. Does anyone know what the retirement date is? Probably stepped up now
ColinSeftel
Colin Seftel 0
Flight Global reports that the UK has now also grounded PW4000-112 engines.
https://www.flightglobal.com/safety/uk-bans-operations-with-pw4000-powered-777s/142548.article
linbb
linbb -3
Oh again too late in posting.
MH370
MH370 -6
(Duplicate Squawk Submitted)

Boeing 777s Powered by PW4000s Grounded Worldwide

Following Japan’s grounding of all Boeing 777s equipped with Pratt & Whitney PW4000-112 turbofans, the U.S. FAA late Sunday said it would issue an emergency airworthiness directive

https://www.ainonline.com/aviation-news/air-transport/2021-02-22/boeing-777s-powered-pw4000s-grounded-worldwide
williambaker08
william baker 3
I was wondering where his post on this was. And they aren’t grounded worldwide only a select number of them.

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