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  • 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.
    Live, from a grassy knoll somewhere near you.

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    • Originally posted by guamainiac View Post
      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.
      Yes, but I would like the best pilot on duty for take-off, landing, and thunderstorms.

      Comment


      • Originally posted by Evan View Post
        Compressor 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.
        Is it possible to re-start the engines after a compressor stall?

        Comment


        • Originally posted by Jpmkam View Post
          Is it possible to re-start the engines after a compressor stall?
          The 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.

          Comment


          • Originally posted by guamainiac View Post
            Evan you should read that Boeing article

            Avoiding Convective Weather Linked to Ice-Crystals ... Icing Engine Events

            It is aimed at tropical humid environments at cruise.
            Yeah, I'd like to see that. Do you have a link?

            Comment


            • It won't link for me .... long story with kids.



              Just Google the Boeing Aero Magazine
              Live, from a grassy knoll somewhere near you.

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              • Originally posted by Evan View Post
                The 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?

                Comment


                • 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 Post
                    It won't link for me .... long story with kids.



                    Just Google the Boeing Aero Magazine
                    Ok, thanks. I had downloaded a similar article a while ago, maybe the same one...?

                    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.
                    What I am really hoping to see with the initial release of information is the OAT and TAT anomalies. That may be the smoking gun as far as ice crystal related issues are concerned.

                    Comment


                    • Originally posted by Fear_of_Flying View Post
                      Would such an event lead to an ACARS message normally, do you think?
                      I 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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                      • Originally posted by Evan View Post
                        I 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.
                        So, 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?

                        Comment


                        • 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.

                          Comment


                          • Originally posted by guamainiac View Post
                            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?
                            In the article I referred to above (and maybe the same one as yours), it recommends to orient the radar to 'look down' for areas of heavy precip at altitudes below freezing temps. It indicates that if such precip is present, then the likelihood of encountering 'invisible' ice crystals at high FL's is high.

                            Comment


                            • Originally posted by Fear_of_Flying View Post
                              So, 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?
                              Again, 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.

                              Comment


                              • Originally posted by Evan View Post
                                Again, 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.
                                From the reports anyway, there was a sudden and significant lifting, nose-up, and this in turn led to the stall. You seem to have it that the compressor stall occurred first, this leading to the pitching up and eventual wing stall (if I'm understanding).

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