Catastrophic engine failure on Flight UA328

[Astronuc]

https://www.flightglobal.com/safety/united-777-suffers-engine-failure-over-denver/142519.article

https://www.flightglobal.com/safety...tained-forward-cowling-missing/142520.article

https://www.ifn.news/posts/united-airlines-flight-ua328-suffers-serious-engine-failure/

The 777 nevertheless returned to the airport and landed safely. "Involved was N772UA, a 26 year-old Boeing 777-200. It was forced to return for an immediate emergency landing, which the pilots carried out safely with no further incident."

"Two similar incidents also occurred with United Airlines in 2016 and 2018. Both cases involved a serious failure of a Pratt & Whitney PW4077 engine on Boeing 777-200 aircraft, the first one being caused by a birdstrike, the second by an oversight during engine maintenance." Maintenance of teh aircraft and engine will certainly be scrutinized.

 

[berkeman]

https://www.ifn.news/posts/united-airlines-flight-ua328-suffers-serious-engine-failure/

Yeah, not what you want to see when looking out of the cabin window...

 

[anorlunda]

Losing an engine in flight is not so bad. All airliners can fly fine with one engine out.

The most scary thing is that the debris can penetrate the fuselage and kill passengers. That really happened a few years ago. But if you are alive enough to look out the window and see that scene, you already survived the most dangerous part.

The second most scary thought is that the cause of the engine failure may not be random. It could be an error that could also cause the other engine to fail the same way.

The third level thought (maybe most scary) is that the engine failure damaged the wing and the wing is about to fall off.

My best wager is that most passengers would not think about such things. They would be thinking about turning on their cell phones to phone home.

 

[Klystron]

The OP articles indicate high-speed fan failure in the engine without noting FOD (foreign object damage).

In the second link the pilots mention using the (emergency) checklists following the engine failure. One of my last assignments at NASA Ames involved modeling the Boeing 777 electronic data recording systems including so-called 'black boxes' for pilot training simulators. A colleague modeled the emergency digital checklists based on potential failure modes including catastrophic engine failure.

Boeing 'went the extra mile' designing and testing 777 pilot information interfaces and automated checklists. It would be interesting to learn how Boeing selected the 777 engines.

 

[Astronuc]

The second most scary thought is that the cause of the engine failure may not be random. It could be an error that could also cause the other engine to fail the same way.

Such an event happened to Cathay Pacific flight 780. https://en.wikipedia.org/wiki/Cathay_Pacific_Flight_780

"After another two hours elapsed, the aircraft was on descent to Hong Kong when, at 05:19 UTC, about 203 kilometres (126 mi; 110 nmi) southeast of Hong Kong International Airport , the aircraft's ECAM displayed "ENG 1 CTL SYS FAULT" and "ENG 2 STALL" within a short period."

The cause of the accident was contamination (filter resin beads) of the fuel taken on board at Surabaya, which gradually damaged both engines of the aircraft. The flight made to the destination, but had to land at a high speed because the No 1 engine was stuck at 74% power. They landed at about 230 knts (265 mph, 436 kmph) well above normal landing speed.

A video dramatization of the flight on the Smithsonian Channel.


https://news.aviation-safety.net/20...-problems-and-emergency-landing-at-hong-kong/

 

[DaveE]

Good early coverage of this from Blancolirio

 

[Vanadium 50]

From UA's web site: "UA328: Your flight is canceled because your plane needs repairs. We're sorry for the inconvenience."

They're not wrong.

 

[Astronuc]

"UA328: Your flight is canceled because your plane needs repairs. We're sorry for the inconvenience."

A wee bit of an understatement.

A new engine and right nacelle, and it will be good as new. Probably have to replace the left engine as well.

 

[Vanadium 50]

I'd also want someone to look at the landing gear and tires. It landed overweight and didn't use thrust reversers.

I'm pretty sure I've been on that aircraft (along with many thousands of others). N772UA is a 772. Sticks in your head.

 

[Dr Transport]

First indication is that a fan blade separated, with a possible second. Very troublesome that the engine cowling sheared off ad separated.xx.

 

[Astronuc]

A new engine and right nacelle, and it will be good as new.

I was being sarcastic here. Probably should have added or

 

[Vanadium 50]

Sarcasm aside, you're probably right - it's nowhere near a loss of an airframe. The extra section to get the passengers to HNL was N773UA, which was the aircraft involved in a similar incident in 2018 flying SFO-HNL.

Engines get replaced all the time.

 

[DaveE]

Also AgentJayZ talks about the engine, if you want more. If you want to learn what's inside a jet engine, he has some other good videos.

 

[Astronuc]

https://www.nbcnews.com/news/us-new...ment-united-flight-328-engine-caught-n1258473

United is the only U.S. airline with the Pratt & Whitney PW4000 in its fleet, the FAA said. United says it currently has 24 of the 777s in service.

https://abc7.com/boeing-777-airplane-engine-faa/10359983/

Airlines in Japan and South Korea also operate planes with the Pratt & Whitney engine. Japan Airways and All Nippon Airways have decided to stop operating a combined 32 planes with that engine, according to Nikkei.

Nikkei reported that Japan's Ministry of Land, Infrastructure, Transport and Tourism also ordered the planes out of service, and the ministry said an engine in the same PW4000 family suffered unspecified trouble on a JAL 777 flying to Haneda from Naha on Dec. 4. It ordered stricter inspections in response

AP and other sources reported that United has grounded their 777s.

United statement:
"Starting immediately and out of an abundance of caution, we are voluntarily and temporarily removing 24 Boeing 777 aircraft powered by Pratt & Whitney 4000 series engines from our schedule. Since yesterday, we've been in touch with regulators at the NTSB and FAA and will continue to work closely with them to determine any additional steps that are needed to ensure these aircraft meet our rigorous safety standards and can return to service. . . . ."

Sarcasm aside, you're probably right - it's nowhere near a loss of an airframe. The extra section to get the passengers to HNL was N773UA, which was the aircraft involved in a similar incident in 2018 flying SFO-HNL.

Engines get replaced all the time.

But as one indicated in a previous post, landing gear and other parts need inspection, but also the NTSB and FAA will have to determine if the primary/root cause was the engine, the nacelle, or some combination. I imagine the planes will be grounded for some time.

I heard one report that pieces of two blades (ostensibly fan) were found. The ABC article cites:

• Two fan blades were fractured

-One fan blade was fractured near the root
-An adjacent fan blade was fractured about mid-span
-A portion of one blade was imbedded in the containment ring
-The remainder of the fan blades exhibited damage to the tips and leading edges

I wonder if the pilot dumped the fuel before landing.

 

[Vanadium 50]

I wonder if the pilot dumped the fuel before landing.

Reports are that he did not.

There are reports of blood inside the engine. That would, if confirmed, suggest a bird strike as likely.

 

[DaveE]

I wonder if the pilot dumped the fuel before landing.

He landed too quickly to have dumped fuel.

 

[berkeman]

I wonder if dumping fuel is contraindicated when you have an engine on fire...

 

[Klystron]

If the flight was non-stop from Denver to Honolulu, the Boeing 777 likely carried maximum regulation mandated fuel amount. Aside from the exposed flames, as questioned above, the time and pumping required to jettison fuel coupled with Denver altitude and return distance to airport likely contraindicated dumping fuel.

United Airline quite lucky in that ~3/4 of the route DEN to HNL extends over open ocean. Incredibly lucky that engine debris fell on land, so recoverable, without any known injuries or related damage.

[Edit 20210328: replaced ambiguous "maximum" with intended meaning of 'regulation required fuel for open ocean commercial flights'. Thanks to post #40.]

 

[Astronuc]

He landed too quickly to have dumped fuel.

Delta flight 89 out of LAX dumped fuel within ~20 minutes after takeoff. "On January 14, 2020, the Boeing 777-200ER conducting the flight had engine problems shortly after takeoff; while returning to the origin airport for an emergency landing, it dumped fuel over populated areas adjacent to the city of Los Angeles, . . . "

https://en.wikipedia.org/wiki/Delta_Air_Lines_Flight_89
https://www.latimes.com/california/...before-it-dumped-fuel-on-an-elementary-school

The United pilot may have chosen not to dump because of the Delta 89 experience. According to Flightradar24, UA 328 was in the air about 23 minutes. Denver airport elevation is ~5430 ft (1655 m). Shortly after lift off the flight was at 7100 ft @0805, ~13450 ft @ 0809, then began descent. It was at ~5825 @0827 just before landing at about 0828.

https://www.flightradar24.com/blog/united-ua328-suffers-engine-failure-departing-denver/

 

[Nugatory]

Much discussion, much of it informed, at https://www.pprune.org/rumours-news/638797-united-b777-engine-failure.html inlcuding a link to YouTube video with the communications with air traffic control.

 

[DaveE]

I wonder if dumping fuel is contraindicated when you have an engine on fire...

This would depend on the aircraft design. It's why some designs dump fuel from the wing tips.

However, the priority if there is a "real" fire is to land ASAP, so I think it's a moot question. There are no common commercial aircraft that can't land overweight, provided they don't have a very short or slippery runway (DEN has long runways). Of course they may trash the tires, brakes, and maybe the landing gear, which is why many don't want to land overweight. Indeed there are common aircraft types that can not dump fuel (737, A320 for example). Also, unless the pilot stuffs that landing, a high-speed rejected take off is the worst case.

In the LA case, most knowledgeable commentators said there was no need to dump fuel. For example, this video from a 777 pilot describes fuel dumping and overweight landing issues.

 

[Astronuc]

There are no common commercial aircraft that can't land overweight, provided they don't have a very short or slippery runway (DEN has long runways).

It depends on the pilot and probably elevation and winds. I've experience smooth landings where one does not feel contact with the runway, and I've experience hard landings where bins drop open, things fall, people get jostled and aircraft bounce two or more times.

I've been through Denver a lot the last several years, on United's 777, which are nice, and plenty of 737s.

 

[DaveE]

It depends on the pilot and probably elevation and winds.

Elevation and wind (as well as other stuff) is planned for in the stopping distance calculation and briefed before take off. What the passengers feel is mostly irrelevant unless the landing is awful, you don't have to land on the numbers. OTOH, there is no limit on how badly a plane can be landed, LOL.

 

[DaveE]

The thing to keep in mind is that you should always be able to immediately return and land from the airport you just left in essentially the same configuration. It isn't safe or allowed to take off if you can't get the plane stopped on the runway if you have to abort at high speed (V1). At V1 you have maximum weight, speeds comparable to landing, and you've already used up a bunch of the runway.

 

[Vanadium 50]

Some pictures:

That'll buff right out.

 

[.Scott]

I like @DaveE posts - especially the video.

I would add one thing:

In the case of UA238, the fire was contained to within the engine - although visible from outside of the engine.
For fires that are external to the aircraft, an important consideration is the flame propagation rate. That rate varies by the type of fuel and the initial fuel temperature, but it is always well below the airspeed of a jet. Though smaller planes may need to speed up to extinguish the flames.

What this means for the discussion above is that once fuel has entered the slip stream, it cannot immediately contribute to an aircraft fire. If it wets the aircraft, then it could a problem after landing.

 

[Vanadium 50]

In the case of UA238

It was UA328. But U-238 certainly is pyrophoric.

 

[trainman2001]

What I've read in Aviation Week is that one blade possibly fractured at the root from a fatigue crack and impacted the other breaking at its midpoint. The containment shields seemed to have worked, but there is concern about why the nacelle casings came off as they did. They're not supposed to do that.

An A380 lost the entire fan when the hub failed. That was a more serious event due to the amount of debris that was flung off. All of the parts ended up in the ice in Greenland. It took almost a year to find the critical hub, but find it they did. It was essential to have it to know what happened.

The bigger the fans get the greater the forces acting on them to pull them apart. P&W is now fielding a geared fan engine which puts the fan power turbine through a planetary gear set so the fan runs at a slower and more efficient speed while the rest of the rotating equipment runs at its optimal speed. These are three-shaft engines so the hp compressor is driven by the hp turbine, the lp compressor runs from its lp turbine at a lower rpm, and the fan turbine spins at a still slower speed. Gearing solves one problem, but does add more mechanical stuff that can fail.

Radial piston engine propellors ran through reduction gears for similar reasons; to enable the prop to turn at its optimal rpm while the crankshaft operates at its faster rpm. In other words, engine makers have lots of experience designing high horsepower gear trains. Another example is the gear train and clutch used by the F-35B STOL version to drive the lift fan. That system is designed to handle 45,000 hp. And like other US produced aviation engines, it's designed to run for 2,000 hours between major overhauls.

 

[Astronuc]

AP reports, "Exam finds multiple cracks in part of United jet’s engine"
https://apnews.com/article/us-news-transportation-5e9f9b7dbc1515fe5a058e7ce65315f7

The National Transportation Safety Board said the blade found “multiple fatigue fracture origins” on the inside surface of the hollow fan blade. The board said “multiple” secondary cracks were found, and that the examination is continuing.

The Pratt & Whitney engine had been used on 2,979 flights since its last inspection, the NTSB said. . . . .

 

[berkeman]

The Pratt & Whitney engine had been used on 2,979 flights since its last inspection, the NTSB said. . . . .

Wow, that sounds like a long time between inspections! What is the standard interval in flight hours between engine inspections? Does routine engine inspection include the fan blades? Or is the inspection interval for them longer? Do they use x-rays to inspect the interior of the blades?

 

[DaveE]

Wow, that sounds like a long time between inspections! What is the standard interval in flight hours between engine inspections? Does routine engine inspection include the fan blades? Or is the inspection interval for them longer? Do they use x-rays to inspect the interior of the blades?

It's certainly not a routine inspection, It's very difficult (expensive) to do. They are inspected with thermal acoustic imaging. Which basically involves launching an acoustic wave into the blade and inspecting for hot spots which are created at fractures. It's only done at engine manufacturers with only a few technicians in the whole country trained to do it. This special inspection is required because they need to find internal cracks. For smaller/simpler blades they can use fluorescent dye inspection, which is much more common and easier to do.

It's not about this style of these turbofan blades, but I thought this video about blade inspection was interesting if you want to geek out a bit.

 

[Astronuc]

Wow, that sounds like a long time between inspections! What is the standard interval in flight hours between engine inspections? Does routine engine inspection include the fan blades? Or is the inspection interval for them longer? Do they use x-rays to inspect the interior of the blades?

We'll have to wait for the NTSB to finalize a report. I imagine that they will look at service life (hours), but more importantly would be cycles of operation.

NTSB docket - United Airlines Flight 328 Boeing 777 Engine Incident
https://www.ntsb.gov/investigations/Pages/DCA21FA085.aspx

An NTSB structures engineer and two investigators from the NTSB's Denver office collected fallen debris with local law enforcement and safety agencies over the next several days. Most of the structure from the inlet cowl and fan cowl doors was recovered and identified. Recovered portions of the inlet cowl, fan cowl door structure, and inlet cowl attach ring were laid out in a hangar, as shown in figure 1. The inlet cowl, fan cowl doors, and thrust reversers will be examined further to map damage and cowl failure patterns after the fan blade failure, and to examine the subsequent progression of fire in the thrust reversers.

Initial examination of the right engine fire damage, as shown in figures 2 and 3, found it was primarily contained to the engine's accessory components, thrust reverser skin, and composite honeycomb structure of the inboard and outboard thrust reversers. Both halves of the aft cowl appeared to be intact and undamaged, and all four pressure relief doors were found in the open position. The spar valve, which stops fuel flow to the engine when the fire switch is pulled in the cockpit, was found closed; there was no evidence of a fuel-fed fire. Examination of the engine accessories showed multiple broken fuel, oil, and hydraulic lines and the gearbox was fractured.

Initial examination of the right engine fan revealed that the spinner and spinner cap were in place and appeared to be undamaged (see figure 5). The fan hub was intact but could not be rotated by hand. All fan blade roots were in place in the fan hub, and two blades were fractured. One fan blade was fractured transversely across the airfoil about 5 inches above the base of the blade at the leading edge and about 7.5 inches above the base of the blade at the trailing edge. The blade's fracture surface was consistent with fatigue. A second fan blade was fractured transversely across the airfoil about 26 inches above the base of the blade at the leading edge and about 24 inches above the base of the blade at the trailing edge (see figure 6). The second blades fracture surfaces had shear lips consistent with an overload failure. The remaining fan blades were full length but all had varying degrees of impact damage to the airfoils.

As a result of this incident, on February 22, 2021, Pratt & Whitney issued Special Instruction 29F-21 providing revised thermal acoustic image (TAI) inspection threshold intervals to 1000 cycles for the first stage low pressure compressor (LPC) blades on the affected engines. On February 23, 2021, the FAA issued Emergency Airworthiness Directive 2021-05-51, which instructs owners and operators of Pratt & Whitney PW4077 and similar type engines to, before further flight, perform a TAI inspection of the first stage LPC blades for cracks and to remove the blade from service if it does not pass the inspection and replace the blade before further flight.

An initial review of maintenance and inspection data for the blade that exhibited fractures consistent with fatigue revealed that it had experienced 2,979 cycles since its last inspection. The subject blade underwent TAI inspections in 2014 and 2016. The TAI inspection data collected in 2016 was examined again in 2018 because of a February 13, 2018, incident involving a Boeing 777 with Pratt & Whitney PW4077 engines (DCA18IA092). The maintenance records group and the powerplants group are reviewing these inspection records to examine the presence and disposition of any anomalies in this TAI data near the fracture initiation point.

The last paragraph refers to 2,979 cycles vs 2,979 flights as reported in the AP article. I don't know if NTSB refers to a flight as a cycle, but when I think if cycles I think of periodic loading and unloading. It could be based on revolutions per unit time integrated over time. The repetitive loading cycle would be complicated. One would have to consider flutter in addition to revolutions.

NTSB News Release
https://www.ntsb.gov/news/press-releases/Pages/mr20210305.aspx

The previous 2018 event (United Airlines N773UA, Flight UA1175, 13 February 2018)
http://aerossurance.com/safety-management/ndi-failures-b777-pw4077-fbo/

 

[Vanadium 50]

The NTSB report was far more illuminating than the newswire reports.

A "cycle" is a takeoff plus landing. There are some edge cases where a flight is 2 cycles. So 2979 cycles in 5 years is 15 hours between cycles. This is not a crazy number for a long-haul plane.

As @DaveE points out, inspections happen much more regularly. This particular kind of inspection is difficult and happens at a lower frequency. As far as I can tell, this (pre-accident) happens whenever the engine is removed for maintenance (20,000 flight hours) or 6500 cycles, whichever comes first. N772UA was probably getting close to the 20,000 hour mark.

 

[Astronuc]

Looking at 6500 cycles, as V50 indicated it could be near 20,000 hrs. If the aircraft (or engine), if it was captured in service for 6.5 to 7 hour flights, then it was approaching 20,000 hrs based on the following average flight durations:
6.5 hrs * 2979 = 19365 hrs
7 hrs * 2979 = 20853 hrs

The duration of the flight is typically 7 hours 10 minutes, but the apparent average time is about 6 hrs 45 min.
Some sample numbers https://flightaware.com/live/flight/UAL328

The return flight (HNL to DEN) has a shorter flight time, ~6.5 hrs.
https://flightaware.com/live/flight/UAL383

UA328, Damage on the ground - http://www.kathrynsreport.com/2021/02/incident-occurred-february-20-2021-in.htmlOn December 4, 2020, a 777-289 (JA8978) operated as JL904 experienced a similar fan blade out failure and partial loss of the fan cowl six minutes after takeoff at an altitude of 16,000 feet (5,000 m).
https://en.wikipedia.org/wiki/United_Airlines_Flight_328#Japan_Air_Lines_Flight_904
https://www.aerotime.aero/26620-japan-airlines-boeing-777-turns-back-after-engine-failure
https://www.aviation24.be/airlines/...suffers-in-flight-uncontained-engine-failure/
https://www3.nhk.or.jp/news/html/20201204/k10012745841000.html (in Japanese)

Japan Transport Safety Board will publish their 2020 annual report in July 2021, and that should have a summary of their investigation of JL904. The investigation report would come later.Metal-Fatigue Signs Link United 777 Fan Blade Failure With 2018 Incident (of course)
https://aviationweek.com/mro/safety...nk-united-777-fan-blade-failure-2018-incident

This matter gets more interesting considering - NTSB to address rare though deadly forward-blade engine failures (in 2019)
https://www.flightglobal.com/in-dep...-forward-blade-engine-failures/135460.article

The National Transportation Safety Board on 19 November will issue conclusions related to a dangerous though infrequent type of turbofan failure that has proved difficult to understand and tough to prevent.

The board is meeting to determine the probable cause of a 2018 in-flight failure of a CFM International CFM56 turbofan on a Southwest Airlines Boeing 737-700.

During that event one fan blade failed, and a portion of that blade flung outward and forward, toward the front of the engine, missing a containment ring designed to prevent failed engine components from exiting the engine.

The blade portion struck the engine’s cowl and engine inlet, sending shrapnel into the fuselage, which broke one window and killed one passenger.

That was a CFM engine rather than a PW engine, yet the failure event seems to be common. A fan blade is ejected forward damaging the engine cowling. Depending on when a fan blade fails, it could be defected inward to the fuselage, or otherwise upward, outward or downward without damaging the fuselage.

https://en.wikipedia.org/wiki/CFM_International_CFM56#Fan_blade_failure

 

[Astronuc]

The fan blade material has been reported as Ti-6Al-4V (UNS R56400), which is a very common Ti alloy.
https://en.wikipedia.org/wiki/Ti-6Al-4V

One interesting comment in the introduction of the article, "However, the poor shear strength and wear resistance of titanium alloys have nevertheless limited their biomedical use." I don't know the basis of the comment. Fatigue life is a concern for the designer and user.

Another interesting comment related to the BEA study cited below - "The alloy is vulnerable to cold dwell fatigue."

https://www.colorado.edu/faculty/ka...27_am_-_asen_5063_2015_final_report_okura.pdf (See section 2)
https://www.bea.aero/uploads/tx_elydbrapports/BEA2017-0568.en.pdfLarge Engine Uncontained Debris Analysis—High-Bypass Ratio Engine Update, DOT/FAA/TC-19/10, April 2019
http://www.tc.faa.gov/its/worldpac/techrpt/tc19-10.pdf

Regarding fatigue life - https://apps.dtic.mil/dtic/tr/fulltext/u2/a444511.pdf