I think I remember reading that the senior pilot likes to be on the flight deck during arrival. One of those Flying mag articles by Abend. His dealt with trips to and from Conus to SA.
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Originally posted by guamainiac View PostI think I remember reading that the senior pilot likes to be on the flight deck during arrival. One of those Flying mag articles by Abend. His dealt with trips to and from Conus to SA.
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Originally posted by Evan View PostCompressor stall is aerodynamic stall of the turbine blades. I've read that heavy ice crystal ingestion could potentially lead to this (or even flameout), as can extreme angle of attack, or a combination of the two. If this occurred, it would not indicate that there is a mechanical issue to address, as the engine is only designed to operate within a normal flight envelope (with engine anti-ice protections for ice-accretion, but probably not large-scale dry ice crystal ingestion). The engines, BTW, are GE's design. Versions of the CF-6-80 are also used on the 767 and 747, so alerts directed at engine performance limitations might also apply to those variants.
My guess, however, is that Der Speigel is hearing whispers and out of their depth again.
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Originally posted by Jpmkam View PostIs it possible to re-start the engines after a compressor stall?
During compressor stall, the engine is still operating and, depending on the cause, might still be producing some thrust or might be experiencing a pressure surge resulting in total loss of compression. If the engine isn't fatally damaged by foreign object ingestion, recovering involves removing the elements that initiated the stall (lowering the AoA, departing the area of ice crystal precipitation, etc.) and restoring axial airspeed. Compressor stalls can quickly lead to severe engine damage, however, if the stall condition cannot be removed.
Assuming for the moment this occurred on AF447, identifying the compressor stall might have been difficult amidst the confusion. Aside from the engine warnings, the telltale signs are EGT and RPM fluctuations, both requiring some attention to the gauges. There can also be a loud bang and noticeable vibration if there is a flow reversal. AFAIK, the procedure for recovery is to lower the nose and reduce thrust setting, which is going to cost you altitude. If your instinct is to maintain altitude while flying above some nasty MCC nightmare, you are going to have to keep the AoA high while losing airspeed, the opposite of what is needed.
Southern Airlines Flt242 was a prime example of what can happen if the thrust levers are not quickly reduced following a surge.
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Originally posted by Evan View PostThe term itself is misleading. The word 'stall' here refers to a disruption of normal axial flow and subsequent pressure imbalances within the engine. It does not have the same meaning as 'stall' in the automotive sense. The engine is still running. It is an aerodynamic term.
During compressor stall, the engine is still operating and, depending on the cause, might still be producing some thrust or might be experiencing a pressure surge resulting in total loss of compression. If the engine isn't fatally damaged by foreign object ingestion, recovering involves removing the elements that initiated the stall (lowering the AoA, departing the area of ice crystal precipitation, etc.) and restoring axial airspeed. Compressor stalls can quickly lead to severe engine damage, however, if the stall condition cannot be removed.
Assuming for the moment this occurred on AF447, identifying the compressor stall might have been difficult amidst the confusion. Aside from the engine warnings, the telltale signs are EGT and RPM fluctuations, both requiring some attention to the gauges. There can also be a loud bang and noticeable vibration if there is a flow reversal. AFAIK, the procedure for recovery is to lower the nose and reduce thrust setting, which is going to cost you altitude. If your instinct is to maintain altitude while flying above some nasty MCC nightmare, you are going to have to keep the AoA high while losing airspeed, the opposite of what is needed.
Southern Airlines Flt242 was a prime example of what can happen if the thrust levers are not quickly reduced following a surge.
Would such an event lead to an ACARS message normally, do you think?
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Well knock me down, it worked. Wife had a computer guy block many links and photos from our computers when the kids were "of age" and now the guy is gone on and fine minds have tried to figure out what he did.
Many of the aviation links my friends send me will NOT open which pizzes me off. Sometimes if they reformat they do.
Sure it's Boeing ... but the depictions and such are topical.
It indicates relights are normally done but perhaps they were making descending into worse conditions?
There are some details in there such as depending on radar returns, the pilots should point radar down to establish what is below .. in order to not fly over a problem.Live, from a grassy knoll somewhere near you.
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Originally posted by guamainiac View PostIt won't link for me .... long story with kids.
Just Google the Boeing Aero Magazine
It described how ice crystal ingestion can form ice accretion in the cooler sections of the low pressure compressor stage. It also identified the weather phenomena where recorded events have occurred. Almost all of them have been in the proximity of convective weather systems where OAT is ISA+10 or more. Sound familiar?
Here, found it...
High-altitude ice crystals in convective weather are now recognized
as a cause of engine damage and engine power loss that affects
multiple models of commercial airplanes and engines. These events
typically have occurred in conditions that appear benign to pilots,
including an absence of airframe icing and only light turbulence.
The engines in all events have recovered to normal thrust response
quickly. Research is being conducted to further understand these
events. Normal thunderstorm avoidance procedures may help
pilots avoid regions of high ice crystal content.
Since 1990, there have been at least 100 jet
engine power-loss events on both commuter and
large transport airplanes, mostly at altitudes higher
than 22,000 feet, the highest altitude where airframe
icing is expected to exist. “Power loss” is defined
as engine instability such as a surge, stall, flameout,
or rollback that results in a sub-idle operating
condition. High-altitude ice crystals are believed
to have caused most or all of these events.
This article explains the ice crystal phenomenon,
how ice crystals cause power loss, the types of
power-loss events, where and when engine powerloss
events have occurred, conditions associated
with ice crystal formation, and recommendations
for flight near convective weather. It also discusses
the importance of pilot reporting of ice crystal
power-loss events.
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Originally posted by Fear_of_Flying View PostWould such an event lead to an ACARS message normally, do you think?
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Originally posted by Evan View PostI don't know what ACARS reports. Since it is maintenance oriented, perhaps a message would indicate high EGT or low thrust indications, or RPM instability. I really don't know.
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Evan, look at the graphic in your post #84 and the diversion.
That diversion is what triggered the search for convective weather. If they did not use the "look down", who knows? Going around one problem only to find themselves in what they thought would be safe. So perhaps they diverted but only into the second problem?Live, from a grassy knoll somewhere near you.
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Originally posted by guamainiac View PostEvan, look at the graphic in your post #84 and the diversion.
That diversion is what triggered the search for convective weather. If they did not use the "look down", who knows? Going around one problem only to find themselves in what they thought would be safe. So perhaps they diverted but only into the second problem?
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Originally posted by Fear_of_Flying View PostSo, supposing there's a good chance an engine stall would have resulted in an ACARS message, which as far as I know there wasn't one, that might bring us back to a plane stall. What sort of nose-up attitude would be necessary to possibly cause that?
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Originally posted by Evan View PostAgain, I'm not aware that ACARS would report anything for compressor stall. We can't deduce anything this way. But I think the possibility of both compressor stall and wing stall are very strong if they encountered the kind of conditions we are describing. The thing is, if so, then the investigation would already have a strong idea of what happened (but not a conclusive finding) and would not have any immediate service bulletin to issue. Yet, we may find that this is what we have long suspected: a recipe of weather factors, aircraft limitations and pilot error (or pilot inability) in coping with it all. Imagine entering severe turbulence, losing airspeed data and autoflight, getting barraged with ECAM messages, not noticing compressor stall indications, not executing the memory items correctly due to inadequate training and a misleading A/THR interface, losing airspeed while the pitch trim keeps raising the AoA... engine stall continues... possibly in both mills... loss of thrust... critical AoA and wing stall with no thrust available... it does sort of all add up. And if it were such a scenario, it is attributable to the pilots, the plane, the weather and the limitations of technology, and none of this can be fixed with a service bulletin.
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