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Wall Street Journal: Airline Regulators Grapple With Engine-Shutdown Peril

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Wall Street Journal: Airline Regulators Grapple With Engine-Shutdown Peril

Old 9th Apr 2008, 12:17
  #21 (permalink)  
 
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So they're coming back to internal icing.
I suggested just that a while ago (allthough maybe with a somewhat different reason, but nevertheless -> engine icing)

http://www.pprune.org/forums/showpos...7&postcount=75

and was ignored.


Be it as it may: In descents, specially after LH flights, I aim for a continuous descent, but with a small part (around FL100) needing a power increase. Just to check. Furthermore if there is the slightest moisture and T's around -10 to +10, it's EngAntiIce on and not only auto. Inflight if I detect crystals around the wiper, again it's EngAntiIce on.
I've done that with JT8s to GE90s and I truly think we will be instructed to do so again in the future by the regulator, manufacturor and airline astronauts - who will then by the way take all the glory of having invented modern aviation again ......
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Old 9th Apr 2008, 17:07
  #22 (permalink)  
 
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@BOAC

No need to fail on ETOPS portion of a flight, every failure counts.

@GMDS This may be the key. Auto feature of anti ice system, the sensor doesn’t necessarily show the same condition as compressor blades.
If there is ignition an unstable condition on the engine will be without consequences.
Adding thrust during descent sheds internal ice.
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Old 9th Apr 2008, 18:37
  #23 (permalink)  
 
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These additional icing hazards near Cbs have been known for some time; several major incidents occurred in the late 1990’s. I am surprised that Mr Hooky did not search the NTSB records for at least two events which they investigated circa 2000.
There are many manifestations of weather related engine malfunctions near Cbs.
At lower altitude there have been events of flameout due to high water content ‘flooding’. Most of the engine types affected have been modified and/or restrictions applied including the use of cont ignition.
At higher altitudes, there have been problems with ice crystals or soft hail leading to ‘mixed phase’ icing. Here, the supercooled water / ice might quickly dissipate the airbleed heating or the liquid water content acts as glue for the ice crystals resulting in a build up. These effects might exceed the engine de-icing capability, or accumulate ice which progressively blocks the compressor resulting in a slow loss of power (overtemp) as opposed to a complete flame out. Modifications to the airbleed increased the anti icing heat flow; it does not suck the ice out as in the report.

The industry has learnt a lot about these unusual conditions, which are normally associated with the larger CBs (but all Cbs are hazardous).
Many of the ice crystal events occurred at the edge or outside of the icing certification boundary (Appx C to CS 25); these conditions are extremely difficult to recreate, thus tanker testing has not been a viable option. A significant amount of research was undertaken by BAE SYSTEMS in the late 1990s in conjunction with the University of Manchester (UMIST) and Lycoming / Honeywell; the information was shared with industry for use in certification guidance and engine modification. However it appears that the information has not reached all of the operating community.

The WSJ report appear to be based on dated information, or the NTSB are revisiting an old problem, or an old problem is resurfacing as pilots forget about the conditions, or new ‘high’ tech engines are not as robust as previous ones. Whatever the reason there is still good cause to avoid Cbs by a large margin and select engine anti icing on early, particularly if descending into icing conditions.

RR engines? Perhaps they are slightly more tolerant; they may not stop, but in ‘coughing’ and ‘spitting’ out ice they may not give full power (not BA038 related … yet).
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Old 10th Apr 2008, 03:36
  #24 (permalink)  
 
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This is not a twin engine or even a single manufacturere issue, it's an all engine issue.

It's a form of water that exists at altitude that can turn into ice inside the engine operating at altitude. It's impossible to keep all ice outside of the engine, so it was anticipated that only moderate amounts would form at any time and when shed would be harmless to the engine. the idea behind the icing tests and certificantion requirements was to demonstrate that continuous operation in the worst icing conditions (for the aircraft) would be of no concern to the engines.

Now they have identified a form of precipitation that is actually worse for the engine then the aircraft, mostly because of the altitude and the work cycle that the engine is operating in.

From my read of the WSJ article two problems can result.


Ice can build internally and when shed it permanently damages the higher RPM aft stage of the compressor. (I understood from the article that this did happen to some RR engine models)

Ice can shed and disrupt the fuel air ratio in the burner resulting in blow outs of the flame. (GE some models and P&W some models)

My understanding is that while the mechanical damage to the blading is permanent, the effects are mostly to the stability or surge margin of the engine and can be mitigated for the remainder of the flight by so called babying of the engine.

The blow out of the burner is also recoverable, by auto-restart features in the FADEC or of course the more intense workload of an inflight restart within the relight envelope. Taken together the fleet has been safe todate. However the level of safety is in question.

What now needs to addressed is how well do these mitigation features work and how many of these events will truly continue to be safe using these extra crutches.. The FAA is now faced with trying to come up with a defined level of capability against this newly defined threat. As in all environmental encounters the capability must necessarily consider a balance between the technically feasible level of capability of the product and the need for a corresponding degree of avoidance of the encounter.

The WSJ article did not define the problem to this depth and that is what the FAA must do. The FAA can not do this by themselves and must engage expertise in both the engineering of the engine designs (operability, FADECs etc.) but also the pilots, Radar, ATC and weather geeks on the avoidance side.

In the short term tweaking engines and operating procedures is simply minimization and not elimination of the risk and in my view not really measureable except by counting number of events per year worldwide (which is outside of the view of the NTSB) On the other hand new certification standards typically won't address today's problem for 10-15 years so we are going to have to live with this newly defined risk. Please do not misunderstand me, this is not a new safety risk (it's been there all along) it is simply now a newly defined risk to be recognized and addressed.
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Old 10th Apr 2008, 08:07
  #25 (permalink)  
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safetypee refers to some UMIST /BAE probes in the late 1990's. I went searching.

First, a correction. UMIST was an autonomous university from 1993 until 2004, so at the time the work took place. It is *now* part of the University of Manchester.

I found the home page of the FAAM aircraft, a BA146 commissioned for performing atmospheric measurements, with a list of all its current projects, including some which might be related. FAAM was commissioned in 2001, though, and is based at Cranfield.

I found one 1999 AIAA paper which might be related, by Strapp et al, including authors from UMIST, BA Regional Aircraft, and RR, entitled Cloud Microphysical Measurements in Thunderstorm Outflow Regions During Allied/BAE 1997 Flight Trials. The experiments were conducted in the southern and midwest US. I don't know if this is the work to which safetypee was referring.

That's all I found so far. Can anybody help with more sources?

PBL
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Old 10th Apr 2008, 17:53
  #26 (permalink)  
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All I found

Was TAMDAR, circa 03-04. NASA trials with a Bae146 that was used to test a troposphere icing model for updating PIREPS. There was flight testing of the sensor and WT research as well.
 
Old 10th Apr 2008, 19:20
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Peter, the trials mentioned in #23 are in part reported by the 1999 AIAA paper.
There were preceding tests with a BAe146 (N.B pre FAAM, but same a/c) flown in Panama. During these tests, in addition to measuring water content, engine anti-ice heat-flow, etc, in the vicinity of Cbs, a few Cb penetrations were made at high level (FL300) and one brief one at lower level. The resulting rough ride / damage suffered in these were the main reasons that the subsequent tests did not go into the heaviest echo regions in the US, but also that the particular icing phenomenon being investigated was occurring well away from the storm core, generally in or under the anvil.
I don’t know of any public report of the Panama tests, but a paper given at a European SETP meeting in Manchester discussed the flight testing and instrumentation aspects of the US tests – sorry no ref or link.
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Old 12th Apr 2008, 13:52
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I agree with GMDS - with immediate effect, we're using manual Nacelle Anti-Ice in the descent, not waiting for the A/D to come out to change the AFM: process could take more than 2 weeks to work through the system, (747-400/GE's).
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Old 12th Apr 2008, 22:03
  #29 (permalink)  
 
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Engine icing problems

It's a long while ago now but when we first got B737-200s in BA I was operating to one of the Greek islands as a very new command. Somewhere over the western Med in the cruise in clear air the airspeed started to fall back rapidly with the thrust levers well up. In desparation I switched on the engine antice and the speed was quickly restored. When I reported this later I was told this was a known characteristic of the PW engines and didn't merit further comment! Plus ca change...
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Old 15th Apr 2008, 05:49
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But a jet engine does not need an ignition system to continue running. The flameout must have another cause, albeit icing related.
Yes, but auto re-ignition may be needed to relight the engine after it has flamed out. Whether it can relight is another question, but it won't re-light without ignition.
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