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United B777 engine failure

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United B777 engine failure

Old 21st Feb 2021, 01:28
  #21 (permalink)  
CCA
 
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Technically contained vs uncontained for certification is only concerned with rotor parts inside the engine. So while the severe vibration causes nacelle parts to fail they are not proof of an uncontained failure.

The fan parts are allowed to impact up to +/- 15 degrees forward / aft radially but must not exit the fan other than out the back after they’ve been stopped so to speak.
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Old 21st Feb 2021, 01:29
  #22 (permalink)  
 
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Don’t have the books here. But last time I read it, uncontained, meant blades coming out at high energy sideways with risk of serious damage to the remaining aircraft.
bits coming through the back or low energy is a successful blade failure containement.
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Old 21st Feb 2021, 01:40
  #23 (permalink)  
 
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568

No, it's a function of the engine. The GE90 was the worst - not coincidentally it also has the largest diameter fan (~120 inches, vs. ~112 for the PW4084 - the GE90-115B is ~122 inches).

It was the FBO test of the GE90 that was the real eye-opener. The blade debris was completely retained, but the vibration was so great that the inlet fell off, with several bits of the engine accessories. FBO is always tricky due to the uncertainties. It's a hugely expensive test to run (basically destroying a highly instrumented engine in the process), so they only want to run it once (assuming it passes) - so you have the statistical uncertainty of a single data point. It's also run statically, so you don't get the effect of the forward speed aero loads (which must be estimated). As Lomo noted, on the 737NG events, the fan blade debris moved forward beyond the containment ring and got into the inlet - I don't think we've ever seen that during a FBO static test so there are apparently other dynamics at play due to forward speed of the aircraft.
Lomapaseo, IIRC correctly the reverser cascades are carbon composite for all the 777 engine installations - so I presume hydraulic fluid (from the T/R actuators) started burning, which then ignited the resin in the carbon composite cascades.
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Old 21st Feb 2021, 01:41
  #24 (permalink)  
 
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The tan covering around the fan casing is acoustic dampening and also intended to capture smaller parts almost like a bulletproof vest. Behind is the accessory case/gearbox which contains or drives (amongst other things) electrical generator, hydraulic pump and engine oil pumps.
So even with the fuel valve shut off there is still plenty of hydraulic oil and engine oil that will burn. Composite materials may have been covered in fuel or oil during the initial failure.
In short, there’s plenty to burn for at least a short period of time.
Engine fire suppression bottles may be less effective with that much cowling missing.
So it may just have to burn itself out.

* This is an exceptionally rare and spectacular failure but it’s not as potentially catastrophic as it looks.
If you’re an ER doctor this is a shallow wound with lots of blood if you will.

No damage to the wing or fuel tanks, no damage to the fuselage, no explosive decompression, no damaged flight controls.
Just really spectacular
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Old 21st Feb 2021, 01:44
  #25 (permalink)  
 
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That's not the definition of an uncontained failure.
The definition of an uncontained failure is high energy debris exiting tangential to the engine (within a few degrees).
Bits coming out the front or back, or the inlet/nacelle falling off, is not considered an uncontained failure. That being said, large bits of the inlet and nacelle coming off is a big no-no since it can do damage to the tail surfaces or to people/structures on the ground.
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Old 21st Feb 2021, 01:52
  #26 (permalink)  
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TD,

Great information as always, sure appreciate that!
Regarding the 737-700, did the Southwest 1380 engine episode also exhibit debris moving forward?
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Old 21st Feb 2021, 01:56
  #27 (permalink)  
 
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The tan covering is the fan containment ring - probably Kevlar. It provides no meaningful acoustic dampening - it's only purpose is to catch and contain fan fragments.
The gearbox is in the core area of the engine (PW4000 and GE90 - Rolls Trent has the gearbox on the fancase), however the oil tank is on the fan case. The fire appears to be in the reverser cascades which as I noted are a carbon composite structure. Likely oil or hydraulic fluid started burning which then ignited the resin the the composite construction.
There is no fire suppression system for the fan case on the PW4000 and GE90 installations - only on the core.
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Old 21st Feb 2021, 02:05
  #28 (permalink)  
 
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tdracer

27 year old aircraft (though engine may not be), 777 number 5. It even spent its first year flying in the development programme It's taken a good while to show up.
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Old 21st Feb 2021, 02:30
  #29 (permalink)  
 
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I agree with the comments that the thread title seems inappropriate, as video evidence so far points to a brilliant example of a successful containment.
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Old 21st Feb 2021, 02:55
  #30 (permalink)  
 
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Following from a few posts above

The engine test is just that, nothing more. The idea is to demonstrate the engine capabilities and provide enough load data to the various installers to use in estimating the loads on their nacelle and their pylon mounts. This goes along way in later analysis to demonstrate to t the FAA that the engine has the capability to be safely installed on multiple aircraft designs. It's then up to the Boeings and Airbus to design their parts to remain safe,

The last thing the engine guy wants is to have some sort of test apparatus that screws up the engine to demonstrate itself and to generate useful load data. Hence interface parts like inlets and nacelles are chosen simply as end-loading attachments. The inlets must operate at zero static speed and max power so they really don't look like flight inlets and then ejected blade pieces just screw themselves forward and out the inlet rather than through the side (just like a turbine exhaust pipe)
The FAA is quite tolerant of the measured load capability in the presence of containment and rundown of the engine debris. Some of us like numbers more than just a one-off test..

On the engine side the worst loads to the mounts and fan bearing supports etc. occur in about 5 rev of the fan, after that it's just run-down loads and changing frequencies to the stuff hung off the engine. This quite often shows up in large oscillations as the plane slows down for landing. Typically nothing to worry about except for passenger comfort

Obviously there are some lessons to be learnt here that will have to wait for the investigation to complete
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Old 21st Feb 2021, 03:00
  #31 (permalink)  
 
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Well...I just watched an interview with aviation gadfly, Greg Feith, who clearly stated that this event was an "uncontained engine failure," so take that for what it's worth.
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Old 21st Feb 2021, 04:24
  #32 (permalink)  
 
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More media:

Former National Transportation Safety Board Chairman Jim Hall called the incident another example of “cracks in our culture in aviation safety [that] need to be addressed”.
Hall, who was on the board from 1994 to 2001, has criticised the FAA over the past decade as “drifting toward letting the manufacturers provide the aviation oversight that the public was paying for.” That goes especially for Boeing, he said.


Seems PPRuNe writers aren't the only ones who have the answers long before the investigators...
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Old 21st Feb 2021, 04:37
  #33 (permalink)  
 
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That's pretty rich, given this was certified over 25 years ago - when he was the chair of the NTSB...
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Old 21st Feb 2021, 05:00
  #34 (permalink)  
 
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With the size of the fan blades on modern high bypass jet engines, we are reaching the stage where a failure will have similar consequences to losing a propellor blade on a piston or turbo prop. If the pitch isn't bought into feather immediately then the engine will do its best to shake itself out of the wing.
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Old 21st Feb 2021, 05:04
  #35 (permalink)  
 
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Lockhart

Are you sure here was a fire light?

It depends on where the pick-ups were installed and where the extinguishing is directed. I don't believe there would be much annunciated for a fire in the reverser
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Old 21st Feb 2021, 05:36
  #36 (permalink)  
 
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The whole engine was vibrating pretty badly. Was there any danger of the engine attach points failing and the whole engine coming off the wing ?
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Old 21st Feb 2021, 05:57
  #37 (permalink)  
 
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The area where the visible part of that fire is located is not a fire zone. The fire detectors on that engine are limited to the core compartment.

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Old 21st Feb 2021, 06:01
  #38 (permalink)  
 
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lomapaseo

For the PW4000 installation, reasonably sure there isn't any fire detection in the fan cowl - and I'm certain there is no fire extinguishing ability (not that it would help with the cowl missing). Fire detection/overheat/extinguishing is all in the engine core - not the fan cowl. For engines where the gearbox is located on the core, the fan cowl is a "flammable leakage zone" (oil and hydraulic fluid) - by design there are no ignition sources, so no fire detection needed.
Edit - I see Dave T beat me to it...
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Old 21st Feb 2021, 06:58
  #39 (permalink)  
 
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Its not like a car where the Engine will most likely stay with the chassis for life. Aircraft Engines get swapped out and replaced during their life cycle. Also now days the Engines are leased by the operator and its separate to the Airframe.
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Old 21st Feb 2021, 07:52
  #40 (permalink)  
 
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Strictly by definition it seems not to be an uncontained engine failure (I rely on the experts to review engine, ot in speculation). However such size of parts departing aircraft is itself an issue both for risk of damage to aircraft and on ground below. From an operational point of view seems to have been well managed.
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