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Malaysia Airlines Loses Contact With 777 en Route to Beijing

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  • Would there be very much fuel in a plane with a destination so relatively close? Just how big a circle is relevant here?

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    • From the NY Times today:

      But the nearly 60-mile width of the band is based on a crucial assumption: that the plane was on autopilot when it ran out of fuel, and that the autopilot was unable to control the plane when the engines stopped. In that case, the plane would have stalled and fallen fairly quickly into the ocean somewhere near where the fuel ran out.
      True or false? Well, if the AP could not hold altitude at speed, would it hold or increase pitch anyway until a stall. No. It should 'give up' and hand over control to the pilot. If the pilot wasn't conscious, would it just maintain the last pitch and power settings until stall. No, the artificial trim aspects of the C*U control law would create an out of trim condition requiring increased aft pressure to hold pitch. AoA protection would also still be active even after fuel exhaustion and would introduce nose down inputs to the flight controls if the AoA became critical. So, my reasoning suggests a slow extended glide following fuel exhaustion in a descent below stall AoA and a rather shallow but high speed (unconfigured) impact with the ocean.

      However:

      But if a skilled pilot was conscious and still at the controls when the fuel ran out, the plane could have glided more than 100 miles before it hit the water. In that case, an undersea debris field would lie far outside the new search zone, which is to be announced soon.
      So, the new search zone assumes a high altitude stall, a la AF447, despite there being nothing to do the relentless up-pulling, and therefore seems to be off by 100 miles from simple logic...

      Help me understand why they would assume a stall.

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      • Originally posted by Evan View Post
        From the NY Times today:

        True or false? Well, if the AP could not hold altitude at speed, would it hold or increase pitch anyway until a stall. No. It should 'give up' and hand over control to the pilot. If the pilot wasn't conscious, would it just maintain the last pitch and power settings until stall. No, the artificial trim aspects of the C*U control law would create an out of trim condition requiring increased aft pressure to hold pitch. AoA protection would also still be active even after fuel exhaustion and would introduce nose down inputs to the flight controls if the AoA became critical. So, my reasoning suggests a slow extended glide following fuel exhaustion in a descent below stall AoA and a rather shallow but high speed (unconfigured) impact with the ocean.

        However:

        So, the new search zone assumes a high altitude stall, a la AF447, despite there being nothing to do the relentless up-pulling, and therefore seems to be off by 100 miles from simple logic...

        Help me understand why they would assume a stall.
        Several questions here...
        What would be the flight control law after dual engine failure and no APU? (RAT only power source) I somehow don't think that it will be C*U and also don't know whhat, if any, envelope protections would be active.

        Even if it goes fully direct law with no protections, the plane would just keep the last trim speed, oscillating around it in a phugoid motion. Assuming that the AP goes off.

        But... What will happen in the roll axis? Because no airplane is perfectly symmetrical, any airplane left at its own (including "no computer" actively flying it) will enter a spiral dive that will typically stabilize at some not-negligible angle of bank. An angle of bank that will require more that 1G to sustain, and since there is nobody to "pull up" the plane will nose down, speed up and generate the extra load factor with speed (instead of with angle of attack). In this motion, the plane will descend quickly and in circles, so it would not go very far away of the point where it run out of fuel.

        And that, of course, assuming that both engines fail simultaneously (or almost). I don't know how the 777 AP left alone would handle the asymmetric thrust of an engine failure.

        --- 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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        • Originally posted by Gabriel View Post
          Several questions here...
          What would be the flight control law after dual engine failure and no APU? (RAT only power source) I somehow don't think that it will be C*U and also don't know whhat, if any, envelope protections would be active.

          Even if it goes fully direct law with no protections, the plane would just keep the last trim speed, oscillating around it in a phugoid motion. Assuming that the AP goes off.

          But... What will happen in the roll axis? Because no airplane is perfectly symmetrical, any airplane left at its own (including "no computer" actively flying it) will enter a spiral dive that will typically stabilize at some not-negligible angle of bank. An angle of bank that will require more that 1G to sustain, and since there is nobody to "pull up" the plane will nose down, speed up and generate the extra load factor with speed (instead of with angle of attack). In this motion, the plane will descend quickly and in circles, so it would not go very far away of the point where it run out of fuel.

          And that, of course, assuming that both engines fail simultaneously (or almost). I don't know how the 777 AP left alone would handle the asymmetric thrust of an engine failure.
          Unfortunately I cannot find a nice, neat list of factors that degrade control law on the B777, but from what I can find it seems that, as long as 1 PFC is active the control law should be at least Secondary, which is still C*U. Even with the RAT and the battery bus 1 PFC should still be powered. Degradation of control law is typically due to data loss, not engine failure (as long as the systems are powered). Envelope protections are lost in Secondary but the artificial speed stability and possibly the high AoA protection should still be in effect.

          I answered the assymetrical thrust question waaay back in this thread. It is not a factor due to the assymetrical thrust compensation on the B777.

          Loss of AP happens when Normal law is lost. WIth no AP and no pilot, would uncommanded roll be corrected (artificial spiral stability)? FBW flies the aircraft to match the intention of the flight controls, so if the yoke is not commanding roll I would expect the FBW to maintain wings level. But control law is mainly concerned with pitch so maybe not...

          But again, I can find nothing from Boeing describing how a fuel exhaustion scenario affects flight control.

          EDIT: The RAT / HOT bus is capable of powering both the left and center PFC's.

          Comment


          • Originally posted by Gabriel View Post
            Several questions here...
            What would be the flight control law after dual engine failure and no APU? (RAT only power source) I somehow don't think that it will be C*U and also don't know whhat, if any, envelope protections would be active.
            I think some answers you find here http://www.pprune.org/rumours-news/5...-lost-431.html

            in post #8618

            Comment


            • Originally posted by Timmerich View Post
              I think some answers you find here http://www.pprune.org/rumours-news/5...-lost-431.html

              in post #8618
              Thanks, absolutely interesting!!! (and not matching what Evan said, mainly I guess because the RAT power is not instantaneously available and even a PFC remains powered, the plane lacks any hydro power to move the controls and hence enforce any control law, so everything gives up: AP off and direct law.)

              Giving credit to suninmyeyes who posted it (and claims to be a 777 pilot), I copy the post in full below and attach the link to the original source:

              As a 777 pilot I, like many others, have wondered how the 777 would perform in the scenario where the pilots were incapacitated and the aircraft ran out of fuel. I had my ideas but there is nothing like seeing it for "real" so we tried this in a 777-2 full motion zero flight time approved simulator.

              We used a zero fuel weight of 175 tonnes. We let it run out of fuel at FL 250 in track hold and alt capture. However it would not make any difference what mode it was in as everything would drop out. In real life one engine uses fractionally more fuel per hour than the other and there is typically a difference between main tanks of a few hundred kilos, so we had a 300 kg difference between the contents of the left and right tank.

              When the first engine failed TAC (Thrust asymmetry compensation) automatically applied rudder. The speed reduced from 320 knots indicated to 245 knots indicated. It was able to maintain 245 knots and FL250. When the second engine failed the rudder trim applied by TAC was taken out and the trim went to zero. The autopilot dropped out and the flight controls reverted to direct mode. The speed initially came back to 230 knots but then the nose started to lower. The nose continued to lower and the rate of descent increased to 4,000 feet per minute, the nose kept lowering and the descent rate increased to 7,500 feet per minute with a bank angle that increased to 25 degrees. The speed at this point had increased to 340 knots indicated, above VMO but there was no horn as it was on limited electrics. About this point the RAT (Ram air turbine) chipped in and the CDUs and copilot's PFD (Primary flight display) came alive. The flight controls stayed in direct mode.The eicas screen was full of messages like pitot heat, flight controls, APU fault (The APU had tried to autostart due double engine failure but failed due no fuel to start it) low fuel pressure etc.

              Then with a max descent rate of almost 8,000 feet per minute the nose started to slowly rise and keep rising. We had dropped to about FL170 but the nose slowly rose up to 6 degrees pitch up and we started climbing at about 3000 feet per minute and the bank angle reduced to only 5 degrees. It climbed back up to FL210 at which point the speed had come back to 220 knots and then the nose dropped down again and we were soon back to descending at 8000 feet per minute. So basically a series of phugoid oscillations with bank angle between 5 and 25 degrees and pitch attitude between about 9 degrees nose down and 6 degrees pitch up. It was losing about 8000 feet and then gaining about 3 or 4000 feet with airspeed fluctuating between 220 and 340 knots.

              We didn't watch it all the way down due time constraints and stopped the experiment at 10,000 feet but it was consistent all the way down. Having watched it I can say with certainty that if the pilots were incapacitated and it ran out of fuel there is no way it could have landed on the water with anything like a survivable impact. Just passing on the info.
              Rumours & News - Malaysian Airlines MH370 contact lost - I think one thing that may have been overlooked, is how far north of Banda Aceh the plane would have had to have flown to avoid Indonesian radar (they said they didnt track it)....So, if we concluded and calculated that the plane ended it's trip sometime not

              --- 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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              • Originally posted by Gabriel View Post
                Thanks, absolutely interesting!!! (and not matching what Evan said, mainly I guess because the RAT power is not instantaneously available and even a PFC remains powered, the plane lacks any hydro power to move the controls and hence enforce any control law, so everything gives up: AP off and direct law.)

                Giving credit to suninmyeyes who posted it (and claims to be a 777 pilot), I copy the post in full below and attach the link to the original source:


                http://www.pprune.org/rumours-news/5...ml#post8407235
                So large phugoid oscillations in a fairly broad descending circle, and here we have an investigation apparently searching in an area based upon the assumption of a stall and flat descent.

                I wonder why direct law. The center and left PFC are fed by seperate power supply assemblies that are in turn fed by the HOT bus (includes the RAT) and each also has a dedicated battery. I see no reason why they would go offline, unless some relay switching delay is involved. The system is designed to be fault passive, meaning tolerant of fault when a pilot is in control. No fuel, no pilot, I guess that didn;t come up in the design briefs.

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                • Originally posted by Evan View Post
                  So large phugoid oscillations in a fairly broad descending circle, and here we have an investigation apparently searching in an area based upon the assumption of a stall and flat descent.
                  ???

                  I don't know that the descent mode has a practical effect on the size and location of the debris field (other than a carefully controlled ditching).
                  Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                  Comment


                  • Originally posted by Evan View Post
                    So large phugoid oscillations in a fairly broad descending circle, and here we have an investigation apparently searching in an area based upon the assumption of a stall and flat descent.
                    Who said stall and flat descent? A large circle will hardly have more of 60NM of radius. A straight line glide from FL400 would be some 120NM long, so half that for an airplane flying random curves seems reasonable.

                    I wonder why direct law. The center and left PFC are fed by seperate power supply assemblies that are in turn fed by the HOT bus (includes the RAT) and each also has a dedicated battery. I see no reason why they would go offline, unless some relay switching delay is involved. The system is designed to be fault passive, meaning tolerant of fault when a pilot is in control. No fuel, no pilot, I guess that didn;t come up in the design briefs.
                    What happens if all PFCs remain powered but the hydro pressure of all hydro systems goes to zero? Do the plane keep normal (or alternate) law even if it has no power to enforce it? Or it reverts to direct?

                    --- 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 ---

                    Comment


                    • Originally posted by Gabriel View Post
                      Who said stall and flat descent? A large circle will hardly have more of 60NM of radius. A straight line glide from FL400 would be some 120NM long, so half that for an airplane flying random curves seems reasonable.
                      Yes, if you know the exact track it was on. I think the 60NM width of the search area is to provide a margin of error for predicted track, not the width of a circling descent. So if you are off by 30NM and the aircraft circled in 30NM miles left or right of LNP track, your search area is off by 30NM. The article states (if it is in fact accurately reported) that the search area assumes a stall and an aircraft falling out such as AF447 did. Yes, I realize that AF447 went significantlt off track as well. What I am trying to say is that first the expected flight behavior of the plane after fuel exhaustion without pilot intervention must be considered, and that does not appear to be the case.

                      What happens if all PFCs remain powered but the hydro pressure of all hydro systems goes to zero? Do the plane keep normal (or alternate) law even if it has no power to enforce it? Or it reverts to direct?
                      You mean a RAT failure as well? The RAT will provide hydraulic pressure to power the flight control surfaces all the way down.

                      Comment



                      • “Specialists have analysed satellite communications information—information which was never initially intended to have the capability to track an aircraft—and performed extremely complex calculations,” Mr Truss said.

                        “The new priority area is still focused on the seventh arc, where the aircraft last communicated with satellite. We are now shifting our attention to an area further south along the arc based on these calculations.

                        “The Australian Transport Safety Bureau will today release a report outlining the basis on which this search area has been defined.”


                        --- 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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                        • The ATSB report mentioned above, explaining how the search area was defined.



                          It's a very interesting report. Detailed, sound, technical, but very understandable and convincing too.

                          The bottom line is that the ATSB has a high confidence that the missing plane hit the water in the 1,120,000 km2 "grey area". But they were asked to defined a "higest probability area" of 60,000 km2 that can be searched within one year, so they started to add enough assumptions until the area got small enough to meet the size goal: The "orange area".

                          Now, "highest probability" doesn't mean "high probability".
                          If we take that the plane hit the water in the grey area with 100% probability, then each and any area of 60,000 km2 will have an about a 5% probability. If the particular orange area selected as "highest probability" had 10 times more probability than the average of the areas of the same size, that would be 50%. Still the toss of a coin that the plane is either there or not there in the orange area.

                          And if searching the orange zone will take one year, searching the grey zone with the same resources will take nearly 20 years.

                          --- 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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                          • So spending the first week of the search on its intended route was a total waste?

                            You dont say....

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                            • Originally posted by Gabriel View Post
                              [...]
                              The bottom line is that the ATSB has a high confidence that the missing plane hit the water in the 1,120,000 km2 "grey area". But they were asked to defined a "higest probability area" of 60,000 km2 that can be searched within one year, so they started to add enough assumptions until the area got small enough to meet the size goal: The "orange area".

                              Now, "highest probability" doesn't mean "high probability".
                              If we take that the plane hit the water in the grey area with 100% probability, then each and any area of 60,000 km2 will have an about a 5% probability. If the particular orange area selected as "highest probability" had 10 times more probability than the average of the areas of the same size, that would be 50%. Still the toss of a coin that the plane is either there or not there in the orange area.

                              And if searching the orange zone will take one year, searching the grey zone with the same resources will take nearly 20 years.
                              It is a good thing that AJ still lets me in here. After a quite severe issue with Brian, I'd wish to see this man in reality, so that I can apologise.

                              Back on topic. Gabriel is an experienced member of jp, probably more experienced than me.

                              But, what he says, one year, is nothing. The MH-B772ER disappeared from the screens on March 8th, 2014. I can remember that very well because of certain personal circumstances.... ...

                              So, on tuesday, we don't search the a/c since one year, but only since 4 months!

                              If the life of humans are concerned, time seems endless. Probably Brian knows what I mean...

                              PS: And what still strikes me, if we have a look at WMKK, there are so many experienced airlines who regularly operate this destination.
                              AF, CX, EK, KL, LH, SQ, TG, et cetera.
                              And no one of us was able to give the proper hint. That somehow is a scratch in my honour.
                              Last edited by LH-B744; 2014-07-06, 01:00. Reason: Not only LH wants to find the B772ER.
                              The German long haul is alive, 65 years and still kicking.
                              The Gold Member in the 747 club, 50 years since the first LH 747.
                              And constantly advanced, 744 and 748 /w upper and lower EICAS.
                              This is Lohausen International airport speaking, echo delta delta lima.

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                              • actually, it was march 7th

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