This time Singapore Airlines Airbus "loses" engines

Henning said:
Failure of the control system.
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What kind of control system has a single point failure critical valve? Airbus is not Microsoft.

Airplanes, especially airliners, are specifically designed to avoid that situation.

You don't have a complete control system failure. You have a partial failure. This includes things like redundant power distribution systems, redundant valves, redundant control modules, and the whole bit. Safety critical design is not at all like designing an iPhone app that can just throw you out when it doesn't understand its inputs.

And "fail open" is a completely inadequate failure strategy. You can flood an engine, and I'd especially be concerned about the fuel/defuel valves failing that way. That could make your flight much shorter than you want. "Any engineer with a lick of sense" would review the failure modes and design a system that is tolerant to the loss of any single component. That does not mean fail open in all cases. It may mean "leave it alone," but once again, not in all cases. For instance, a wing fire that takes out the fuel system wiring harnesses might do better if the isolate valves failed closed….
 
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MAKG1 said:
What kind of control system has a single point failure critical valve? Airbus is not Microsoft.

Airplanes, especially airliners, are specifically designed to avoid that situation.

You don't have a complete control system failure. You have a partial failure. This includes things like redundant power distribution systems, redundant valves, redundant control modules, and the whole bit. Safety critical design is not at all like designing an iPhone app that can just throw you out when it doesn't understand its inputs.

And "fail open" is a completely inadequate failure strategy. You can flood an engine, and I'd especially be concerned about the fuel/defuel valves failing that way. That could make your flight much shorter than you want. "Any engineer with a lick of sense" would review the failure modes and design a system that is tolerant to the loss of any single component. That does not mean fail open in all cases. It may mean "leave it alone," but once again, not in all cases. For instance, a wing fire that takes out the fuel system wiring harnesses might do better if the isolate valves failed closed….
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Sure, parallel redundant systems is another way to acceptably engineer it so a failed valve cannot starve the engine of fuel in the plane. My point on this whole regards was that I did not believe that a mechanical/electronic/aircraft failure in the fuel delivery system is causal here. My suspicions fall to weather, but no one answered on if it was possible for turbulence to knock the engine off line.
 
Henning said:
Sure, parallel redundant systems is another way to acceptably engineer it so a failed valve cannot starve the engine of fuel in the plane. My point on this whole regards was that I did not believe that a mechanical/electronic/aircraft failure in the fuel delivery system is causal here. My suspicions fall to weather, but no one answered on if it was possible for turbulence to knock the engine off line.
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Turbulence may possibly flame out a turbo fan engine, but it would be a mother of a turbulence to do that.
 
RotorAndWing said:
Turbulence may possibly flame out a turbo fan engine, but it would be a mother of a turbulence to do that.
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At least two three notable cases of hail and/or rain causing flameout, though not sure how relevant they are to the incident in the first post:

http://en.wikipedia.org/wiki/Southern_Airways_Flight_242
http://en.wikipedia.org/wiki/Garuda_Indonesia_Flight_421
http://en.wikipedia.org/wiki/TACA_Flight_110

Wikipedia lists some other notable flameout incidents in its page on the subject and possible causes of flameouts:

http://en.wikipedia.org/wiki/Flameout

[Edited to add TACA Flight 110.]
 
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Jim Logajan said:
At least two three notable cases of hail and/or rain causing flameout, though not sure how relevant they are to the incident in the first post:

http://en.wikipedia.org/wiki/Southern_Airways_Flight_242
http://en.wikipedia.org/wiki/Garuda_Indonesia_Flight_421
http://en.wikipedia.org/wiki/TACA_Flight_110

Wikipedia lists some other notable flameout incidents in its page on the subject and possible causes of flameouts:

http://en.wikipedia.org/wiki/Flameout

[Edited to add TACA Flight 110.]
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Now we are throwing hail into the equation, which yes, will shut down an engine primarily through engine damage. Hail is like throwing rocks through the engine and has the same results. In the incidents noted above it was the hail that precluded the flameout, not turbulence or rain.

Back on topic, the Singapore 330 was at FL390, and the chance of hail is fairly slim, and no chance of heavy precipitation at that altitude.
 
Uh...no chance of heavy precipitation at FL 390? BTDT. 50K plus TRW HEAVY rain, small hail, severe turbulence, white caps in my coke, and we were ten miles plus from the edge of the storm (with zero place to deviate). Wind blowing the stuff to us.

Something no one has mentioned is Ozone. Previous company had a Lear 23 trying to climb at 410 between to cells and according to the engineers later, a suspected cloud to cloud lightening bolt was so close that the aircraft injested a "slug" of pure ozone. That was their theory. Every AC breaker popped and they descended into the cells. I flew with the Captain and he thinks they rolled inverted fives times trying to get clear. Broke out and started one engine after resetting CB's and landed in Vernon TX.

Transport fuel systems can switch feed for engines manually or automatically. My airplane pumps as much as 14.2 K into the tail for CG optimization and the oral answer for how it does all the fuel transfers is "magic". It also uses capacitance fuel level transducers (multiple per tank) and sends this information to a central sending unit - anyone see the problem? The sending unit sends the information received from ONE of the level transducers to the big computer and it may be a bad signal. Try being about 800 miles from the coast of Ireland, at night and the fuel level drops to zero from about 80K lbs. all three engines go to idle and due to other redundancy do not shutdown. FMC commands throttles to idle, speed starts dropping and THEN the good transducer sends a signal and magically you have 80K lbs of fuel and the throttles come up and all is well until it does it again. Not a fun time and no one has the systems knowledge available to cover this.
 
MD11Pilot said:
Uh...no chance of heavy precipitation at FL 390? BTDT. 50K plus TRW HEAVY rain, small hail, severe turbulence, white caps in my coke, and we were ten miles plus from the edge of the storm (with zero place to deviate). Wind blowing the stuff to us.

.
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So you had rain with the OAT of -55 C?
 
MD11Pilot said:
Transport fuel systems can switch feed for engines manually or automatically. My airplane pumps as much as 14.2 K into the tail for CG optimization and the oral answer for how it does all the fuel transfers is "magic". It also uses capacitance fuel level transducers (multiple per tank) and sends this information to a central sending unit - anyone see the problem? The sending unit sends the information received from ONE of the level transducers to the big computer and it may be a bad signal. Try being about 800 miles from the coast of Ireland, at night and the fuel level drops to zero from about 80K lbs. all three engines go to idle and due to other redundancy do not shutdown. FMC commands throttles to idle, speed starts dropping and THEN the good transducer sends a signal and magically you have 80K lbs of fuel and the throttles come up and all is well until it does it again. Not a fun time and no one has the systems knowledge available to cover this.
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The MD-11's have some "interesting" system architecture to say the least. :rolleyes:
 
RotorAndWing said:
Turbulence may possibly flame out a turbo fan engine, but it would be a mother of a turbulence to do that.
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They were flying in an area with mother turbulence though, and were reportedly in bad weather so that still leaves it as a potential.:dunno:
 
MD11Pilot said:
Yep, it was coming from lower and being thrown up and out. Lot of slush also. Ice crystals etc. not a regular or fun time.
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Hmmmmm, ok. For water to stay liquid in -50C air is, well.....

1316713879_castle_reaction_zps3jbjwk4y.gif



MD11Pilot said:
Lots of weird stuff happens around the equator.
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Since that's where I spend the majority of my time flying (ITCZ) yes, it's very interesting flying.
 
RotorAndWing said:
Hmmmmm, ok. For water to stay liquid in -50C air is, well.....

1316713879_castle_reaction_zps3jbjwk4y.gif





Since that's where I spend the majority of my time flying (ITCZ) yes, it's very interesting flying.
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And that is why I said it was weird! As to whether it was "rain" or slush...it was very heavy and flowed up the windscreen as it was illuminated by lightning. We also got "ice detected" message...in -50C where it SHOULD have been ice crystals. YES, ice crystals can build up to change the ice detect frequency but I usually never see that up there.

From Skybrary

Supercooled Water Droplets
Categories: Operational IssuesWeather
Article Information
Category: Weather Weather
Content source: SKYbrary Logo SKYbrary.gif
Content control: EUROCONTROL Logo EUROCONTROL.gif
WX
Tag(s) Atmosphere
Contents [hide]
1 Definition
2 Description
3 Ice Crystals
4 Latent Heat
5 Supercooled Large Droplets (SLD)
6 Related Articles
Definition

Water droplets which exist in liquid form at temperatures below 0°C.
"Supercooled large droplets (SLD) are defined as those with a diameter greater than 50 microns” - The World Meteorological Organization.
“Supercooled Large Drop (SLD). A supercooled droplet with a diameter greater than 50 micrometers (0.05 mm). SLD conditions include freezing drizzle drops and freezing raindrops.2 - FAA AC 91-74A, Pilot’s Guide to Flight in Icing Conditions
Description

The freezing point of water is 0°C but it might be more accurate to say that the melting point of ice is 0°C. This is because, for a number of complex reasons, water exists in liquid form well below 0°C. Supercooled water exists because it lacks the ability to complete the nucleation process. Two of the factors influencing the freezing of supercooled droplets are the need for a freezing nuclei (usually ice crystals) and latent heat which is released when water freezes.
Ice Crystals

In "cold" clouds, where the temperature is below 0°C, ice crystals and supercooled droplets co-exist. In these 'mixed' clouds, the air is close to being saturated with respect to liquid water, but is super-saturated (an unstable phase) with respect to ice. Consequently, in mixed clouds, ice crystals grow from the vapour phase much more rapidly than do the nearby droplets. This is usually known as the Bergeron - Findeisen or "ice crystal" process.
At temperatures between 0°C and -15°C most clouds are composed of supercooled water droplets.
Between -15°C and -40°C most clouds contain a mixture of ice crystals and supercooled water droplets.
Below -40°C almost all clouds consist entirely of ice crystals, with the notable exception of Cumulonimbus clouds, in particular the “anvil clouds”.
Supercooled droplets are in an unstable state and usually start to freeze when brought into contact with ice crystals and particles with a similar structure to an ice particle (freezing nucleus). The ice crystals may form directly from water vapour in the cloud or fall into the cloud from above.
Latent Heat

When water freezes, latent heat is released. This means that if a whole droplet was to freeze instantaneously, the latent heat liberated would, unless the initial temperature was below -80°C, raise the temperature of the droplet above 0°C which would be contradictory since ice cannot exist above 0°C. In fact only a small proportion of the drop freezes instantaneously, not more than enough to raise the temperature above 0°C. Further progressive freezing takes place as the droplet loses heat by evaporation and conduction.
When freezing of supercooled droplets takes place spontaneously, the larger water droplets tend to freeze more readily than smaller droplets. The freezing of droplets becomes more probable as the temperature decreases.
In aviation, small droplets will tend to freeze on the wing rather instantaneously, forming rough, white, opaque, ice deposits which are relatively easy to remove, called rime ice.
The latent heat released in the freezing process serves to warm the air immediately surrounding the droplet relative to the air surrounding the cloud, thereby promoting instability and upward development of the cloud.
Supercooled Large Droplets (SLD)

A term often used in discussions on in-flight airframe icing is the "supercooled large droplet". If an SLD is large enough, its mass will prevent the pressure wave traveling ahead of an airfoil from deflecting it. When this occurs, the droplet will encounter the airfoil surface, and because of its size only the part of the drop immediately hitting the airfoil may freeze. The rest of the droplet will be swept back by the airflow, and the droplet will freeze in the same manner as on initial contact, until all the droplet is frozen. This swept-back ice formation tends to leave a transparent, smooth, relatively difficult ice to remove, and is called clear ice.
 
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MD11Pilot said:
And that is why I said it was weird! As to whether it was "rain" or slush...it was very heavy and flowed up the windscreen as it was illuminated by lightning. We also got "ice detected" message...in -50C where it SHOULD have been ice crystals. YES, ice crystals can build up to change the ice detect frequency but I usually never see that up there.

From Skybrary

Supercooled Water Droplets
Categories: Operational IssuesWeather
Article Information
Category: Weather Weather
Content source: SKYbrary Logo SKYbrary.gif
Content control: EUROCONTROL Logo EUROCONTROL.gif
[...]
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I think these two long articles may be relevant; I've quoted some highlights:

http://aviationweek.com/bca/high-altitude-ice-crystal-icing
Many business jets have the capability to climb quickly into the mid-40 flight levels and cruise far above most weather. It can be tempting to sit back, enjoying the generally clear skies at these altitudes and taking relief that the weather below us can’t hurt us. Unfortunately that “comfort zone” was temporarily burst on Nov. 28, 2005, when the dual-engine flame-out of a Beechjet rudely awakened the business jet community. Answers to important questions were not readily available in the immediate aftermath. Many of us wondered what could have caused two engines to simultaneously fail. Were these failures limited to the Pratt & Whitney Canada JT15D design, or could this happen to other engines?
According to NASA scientists Harold E. Addy Jr. and Jospeh P. Veres of the Glenn Research Center in Cleveland in “An Overview of NASA Engine Ice-Crystal Icing Research,” (NASA/TM-2011-217254, November 2011), “It is a problem whose frequency is alarmingly high…. Evidence indicates that engine icing incidents caused by ice accreting inside the core of jet-based engines have been occurring for over two decades.”
​
[...]
Generally the events occurred from ISA+10C to ISA+20C. In fact, most of the events occurred outside the FAR Part 25 Appendix C envelope for engine certification in icing conditions. Aircraft were in the vicinity of convective clouds/thunderstorms, although flight crews reported no flight-radar echoes at the altitude of the event. Precipitation in the form of “rain” was noted on the windscreen, which at first perplexed investigators because the events occurred at altitudes far higher than where supercooled raindrops would exist. No airframe icing was noted. It has since been determined that the “rain on the windscreen” was actually the melting of the high-altitude ice particles.
Events commonly occurred while diverting around a flight-level high reflectivity region associated with an isolated thunderstorm core, as well as in the broad anvil outflow regions from clouds associated with convective storm complexes and tropical storms. Overshooting tops (dome-like protrusions from the top of an anvil cloud) are an indicator that significant convection is occurring and that ice crystal icing may be possible. Downwind from the tops of large areas of convective clouds, which are often signified by the visible anvil shape, is the main risk area for encountering high crystal concentrations.
​
Avoiding Convective Weather Linked to Ice-Crystal Icing Engine Events
http://www.boeing.com/commercial/aeromagazine/articles/qtr_01_10/5/
Engine events most commonly occur at altitudes of 20,000 to 35,000 feet at temperatures ranging from ‑10 degrees C to -40 degrees C. However, some outlier events have occurred at altitudes as low as 9,000 feet with a temperature of ‑8 degrees C and at altitudes as high as 41,000 feet with temperatures down to ‑63 degrees C.

​
[...]
Based on an analysis of the ice crystal engine event database, Boeing has developed the following recommendations to help flight crews avoid regions of HIWC:

  • During flight in instrument meteorological conditions (IMC), avoid flying directly above significant amber- or red-depicted map weather radar regions.
  • Use the weather radar gain and tilt functions to assess weather radar reflectivity below the airplane.
For example, if an airplane is flying in IMC above the freezing level and there are amber or red radar returns in the vicinity or cloud tops up to the tropopause, or the airplane is known to be in a convective cloud, regions of HIWC may be in the area. In this scenario, the pilot should point the radar down to look below the freezing level. If amber and red areas indicating heavy rain are detected below the freezing level, HIWC areas are possible above these low-level moderate to heavy rain regions. Under these conditions, the pilot should consider evasive action.
​
 
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