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swiftair Md-80 missing

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  • #91
    Originally posted by Gabriel View Post
    The TAT plot puzzles me...
    TAT anomaly is a sign of ice crystal icing. Although it usually causes readings around 0°C as the crystals melt on the sensor.

    Most ITCZ ice crystal events have occured in ambient temperatures in the -30°C to -40°C range, so TAT at -20°C would seem to allow for that, no?

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    • #92
      Boeing literature:

      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, flame* out, 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.

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      • #93
        The TAT plot here lacks the anomaly signature that is commonly seen during ice crystal icing (which is a rather sudden 0°C reading). Also, the corresponding elevator and pitch plots suggests that they were not in deep stall so the idea of a stalled wing affecting the engines to this degree seems remote.

        However, If this was a case of conventional icing in mixed-phase conditions, you might expect to see what the engine plots are showing: a sudden shedding into the core causing surge and rollback; a corresponding rise in EGT (indicating a surge, not a flameout) pilots bringing thrust to idle and cycling fuel valves and restarting at around 10,000ft.

        The best theory I have is that they encountered glaciated and mixed-phase icing which first rendered the EPR PT2 sensor innacurate due to ice crystal ingestion and caused the EPR Limit to steadily reduce engine speeds and the AP to steadily increase AoA. At the reduced N1, the engines would have been more vulnerable to conventional ice ingestion than they would have been at their normal cruise power levels. Then, a sudden ingestion of shedding ice caused a nearly simultaneous surge in both engines. The crew, focused on the problem, let the AP approach stall and then, when it disconnected, they failed at stall avoidance and by the time the engines were producing thrust again they could not exit a fully developed stall.

        This might also explain the lack of comms.

        The puzzling aspect to this theory is that they were at a negative pitch the entire time of the supposed surge recovery and were recovering airspeed and thrust but did not recover from the roll and pull out of the dive. I am thinking spacial disorientation had a strong part in this. During the power loss there would have been a period of minimal instrumentation in a very dark cockpit.

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        • #94
          Originally posted by Evan View Post
          The puzzling aspect to this theory is that they were at a negative pitch the entire time of the supposed surge recovery and were recovering airspeed and thrust but did not recover from the roll and pull out of the dive. I am thinking spacial disorientation had a strong part in this. During the power loss there would have been a period of minimal instrumentation in a very dark cockpit.
          A few parallels to AF447 there. From the report:

          Between May and October, there is an inter-tropical front over Africa. This front is an area of conflict between the masses of dry air over the Sahara and the masses of moist air from the Atlantic. The contrast causes the development of thick convective clouds of the cumulonimbus type and heavy rainfall (monsoon rains).

          Over West Africa, the monsoon is often associated with violent squall lines as well as vast cloud formations that extend over several degrees of latitude and longitude. These disturbances cross the continent from east to west at intervals of three to five days. This phenomenon is called the easterly wave. The activity of these waves is subject to diurnal variations. They develop between 12 h 00 and 18 h 00, are at a maximum at the start of the night, weakening between 3 h 00 and 9 h 00.

          The size of the thermal contrasts and the amount of moisture generate storm cells whose horizontal dimension can be hundreds of kilometres and whose vertical development extends throughout the atmosphere, often exceeding 15,000 metres.

          In the evening and night of 23 July 2014, the inter-tropical front was positioned over northern Mali.

          Interesting that they decided not to take their originally filed route:

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          • #95
            Reading the ATC transcripts, I guess the controllers gave the flight the more direct route to EPEPO and they took it.

            Cargolux 805 that departed just before them provides some interesting clues also. They climb initially to FL370 on the same route, and later ask for FL410

            #Ouaga CCR# Oui heu, le Cargolux demande le niveau 410 et Air
            Algérie niveau 310
            01 h 12 min 21 #Niamey CCR# Non le 370 s'il vous plait, j'ai du trafic c'est pour cela que je l'ai limité initialement au 370
            Niamey says there is traffic and Cargolux must stay at 370. He copies 310 for the accident flight. Presumably the 744 didn't have any trouble passing through that area at FL370. They don't seem to report any course deviations either.

            The other Air Algerie flight (#5005) that passed through the same area as the accident flight was also at FL370.

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            • #96
              Originally posted by Leftseat86 View Post
              Reading the ATC transcripts, I guess the controllers gave the flight the more direct route to EPEPO and they took it.

              Cargolux 805 that departed just before them provides some interesting clues also. They climb initially to FL370 on the same route, and later ask for FL410



              Niamey says there is traffic and Cargolux must stay at 370. He copies 310 for the accident flight. Presumably the 744 didn't have any trouble passing through that area at FL370. They don't seem to report any course deviations either.

              The other Air Algerie flight (#5005) that passed through the same area as the accident flight was also at FL370.
              Most ice crystal icing (glaciated) and mixed-phase (ice crytal and supercooled water) incidents in the ITCZ occur between FL280 and FL310, according to the Boeing literature. This seems to be the goldilocks zone.

              Does anyone know the if the temps were above ISA that day?

              Comment


              • #97
                Originally posted by Evan View Post
                Most ice crystal icing (glaciated) and mixed-phase (ice crytal and supercooled water) incidents in the ITCZ occur between FL280 and FL310, according to the Boeing literature. This seems to be the goldilocks zone.

                Does anyone know the if the temps were above ISA that day?
                And per the report none of it would show up on their weather radar at all.

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                • #98
                  Another pair of iced-up pitots (except this time it was those of the engines).
                  Another stall.

                  Aviation Herald - News, Incidents and Accidents in Aviation

                  --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                  --- Defend what you say with arguments, not by imposing your credentials ---

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                  • #99
                    Originally posted by Gabriel View Post
                    Another pair of iced-up pitots (except this time it was those of the engines).
                    Another stall.

                    http://avherald.com/h?article=477c75de/0004&opt=0
                    The PT2 sensors again.

                    The recorded data suggest that there has been no stall recovery done by the crew. Following the roll and nose down there are control inputs recorded to roll the aircraft right and pull the nose up.
                    Apparently no unusual attitudes training here either. But what about approach to stall? The report summary doesn't mention anything.

                    Comment


                    • Originally posted by Evan View Post
                      The PT2 sensors again.(...)
                      Again? Sorry, don't recall the last time, please refresh my memory, Evan.


                      Originally posted by Evan View Post
                      (...)Apparently no unusual attitudes training here either. But what about approach to stall? The report summary doesn't mention anything.
                      Well - it's only a preliminary report. Maybe/hopefully all aspects will be covered in the full report.

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                      • Originally posted by Peter Kesternich View Post
                        Again? Sorry, don't recall the last time, please refresh my memory, Evan.
                        Air Florida Flt 90, the 737 that plunged into the Potomac. The investigation suspected an iced PT2 probe was involved. There have also been a number of incidents involving this phenomena at altitude. CASA has issued a bulletin regarding the danger. This should be a well-known danger to any pilot operating a JT8D equipped aircraft.
                        Originally posted by AV Herald
                        The BEA reported that there had been 2 similiar occurrences before: On Jun 4th 2002 a Spirit Airlines MD-82 registration N823NK was in flight at FL330 in daylight out of clouds when power was lost in both engines due to overestimated EPR values due to ice crystals blocking both pressure sensors at the engine inlet, the crew descended the aircraft, activated the anti-ice systems and continued to destination, and on Jun 8th 2014 a Swiftair MD-83 registration EC-JUG was in level flight at FL330 in daylight above cloud layer, when the crew noticed the problem, engaged the anti-ice clearing the problem before reaching stall and continued to destination.
                        The PT2 probe measures pressure at the compressor face and that data is used to calculate EPR. An erroneous reading due to blockage will result in an erroneous EPR calculation and a reduction in available thrust.

                        The tip-off would be all the other readings (i.e. N1, EGT, Fuel Flow) being unusually low. I think N1 is the most obvious indication. And of course decaying airspeed...

                        Essentially, what I think we have here is an AF 447 type of ITCZ event in Unreliable EPR form, so the crew would have to be alert and respond correctly to a disorienting situation.

                        They weren't, They didn't.

                        Comment


                        • Originally posted by Evan View Post
                          Air Florida Flt 90, the 737 that plunged into the Potomac. The investigation suspected an iced PT2 probe was involved. There have also been a number of incidents involving this phenomena at altitude. CASA has issued a bulletin regarding the danger. This should be a well-known danger to any pilot operating a JT8D equipped aircraft.
                          (...)
                          Oh okay - I didn't consider Air Florida 90, because the Swiftair scenario was so different.

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