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  • Originally posted by Evan View Post
    I was wrong about one of my earlier assumptions concerning the abuse of FLCH in this case. Instead of using an MCP altitude that is too low and unsafe (such as 0') to achieve and maintain idle thrust and a rapid altitude change, this pilot had left in an MCP altitude that was too high (3000', well above their present altitude). This resulted in the A/P commanding pitch up, which prompted the confused pilot to disengage the A/P.
    And prompted your confusion too.

    Tell me one thing: In a "pitch controls speed" mode, why would the plane pitch up for the insignificant reason that you selected a higher altitude?
    Answer: it wont. The pitch holds the speed, not the altitude. The only function to set an altitude in FLCH is to the system (FD and AT) to revert to ALT HOLD (FD) and SPEED HOLD (AT) once and if the selected altitude is achieved.

    The reason why the plane climbed when he selected FLCH is because the plane was flying faster than the SPEED (not altitude) left in the MCP. The FD was commanding pitch up to slow down, and it would have done so even if the selected altitude was lower that the airplane's altitude.

    The MCP reference speed was also too high, prompting the A/T to increase thrust (as it was in THR mode)
    Nope. The selected altitude was too high, and the thrust insufficient for the climb, what prompted the A/T to increase thrust to be able to reach the selected altitude, otherwise, once the plane slowed down to the selected speed, it would have pitched down and descended again to hold the speed.

    Where the selected speed was too high? The selected speed was below the actual speed all the time (until the plane became low and slow at the end).

    In short, they were in a "pitch holds speed" mode.

    --- 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


    • I'd hope you guys re-read what I said about overload. This is a CLEAR, CLEAR example of a crew panicking, and making selections they would not make when they had a clear mind.

      This is not a crew not knowing how the system works, but a crew that didn't have the brainspace to apply that knowledge because they had allowed themselves to get into a situation in which they were overloaded.

      Instead of using an MCP altitude that is too low and unsafe (such as 0') to achieve and maintain idle thrust and a rapid altitude change, this pilot had left in an MCP altitude that was too high (3000', well above their present altitude).
      Not quite true. They didn't 'leave' an MCP altitude, they intentionally set it. This is normal procedure once you're on an approach, either with the G/S captured, in V/S, or in VNAV (with other conditions met). The 3000ft is the missed approach altitude. The idea is when you go around the system is set to capture the missed approach altitude. This is normal procedure for all approaches. Of course you would never be pressing FLCH once this was set...


      This resulted in the A/P commanding pitch up, which prompted the confused pilot to disengage the A/P. The MCP reference speed was also too high, prompting the A/T to increase thrust (as it was in THR mode), which in turn prompted the pilot to manually retard the thrust levers and thereby change the A/T mode to HOLD. This is further evidence of his inadequate training on the AFCS.
      MCP speed reference was ok. The A/T increased thrust because it was trying to achieve the climb that was commanded by the system (below an altitude with FLCH selected makes it attempt to climb to that altitude, and it applies thrust to do so). Gabriel explains well the way it is speed on elevator, and it pitches for speed - the thrust is used to do the climb/descent. When he pulls the thrust back, the AFDS can no longer achieve the climb, and so it continues to pitch for speed. A valuable protection.

      The pilot was overloaded and was pressing buttons to try and make something happen. It was not a logical thought process.

      Because FLCH SPD is designed to achieve a selected flight level, entering that altitude is part of the modal sequence. Obviously he didn't think to notice that altitude shown on the MCP when he chose FLCH, choosing it purely for the A/T effect he was expecting (IDLE).
      He chose it probably because he'd seen it used when high on an approach before. It is sometimes appropriate to get yourself onto an approach. But not for landing. Overload.

      Comment


      • Originally posted by MCM View Post
        I'd hope you guys re-read what I said about overload. This is a CLEAR, CLEAR example of a crew panicking, and making selections they would not make when they had a clear mind.

        This is not a crew not knowing how the system works, but a crew that didn't have the brainspace to apply that knowledge because they had allowed themselves to get into a situation in which they were overloaded.



        Not quite true. They didn't 'leave' an MCP altitude, they intentionally set it. This is normal procedure once you're on an approach, either with the G/S captured, in V/S, or in VNAV (with other conditions met). The 3000ft is the missed approach altitude. The idea is when you go around the system is set to capture the missed approach altitude. This is normal procedure for all approaches. Of course you would never be pressing FLCH once this was set...




        MCP speed reference was ok. The A/T increased thrust because it was trying to achieve the climb that was commanded by the system (below an altitude with FLCH selected makes it attempt to climb to that altitude, and it applies thrust to do so). Gabriel explains well the way it is speed on elevator, and it pitches for speed - the thrust is used to do the climb/descent. When he pulls the thrust back, the AFDS can no longer achieve the climb, and so it continues to pitch for speed. A valuable protection.

        The pilot was overloaded and was pressing buttons to try and make something happen. It was not a logical thought process.



        He chose it probably because he'd seen it used when high on an approach before. It is sometimes appropriate to get yourself onto an approach. But not for landing. Overload.
        Ooof, yeah, I got it all backwards didn't I. The MCP speed was too low, the MCP altitude (set for go-around) was too high, so altitude initiated thrust and speed initiated pitch. Speed-on-elevator.

        MCM, when you properly select FLCH, don't you also set proper values for speed and altitude? What I meant is that they left in the GA altitude, which would cause FLCH to engage as a climb, not a descent. I understand your point about being overwhelmed but it seems pretty ignorant to be 'pressing buttons' without setting the criteria that determine the AP's reaction to the selected mode. At least in the other instances I've read about where FLCH is abused for fast descent, the pilots knew that a lower altitude (like 0') was they key to doing this.

        Comment


        • Originally posted by Evan View Post
          Ooof, yeah, I got it all backwards didn't I. The MCP speed was too low, the MCP altitude (set for go-around) was too high, so altitude initiated thrust and speed initiated pitch. Speed-on-elevator.
          Correct.

          MCM, when you properly select FLCH, don't you also set proper values for speed and altitude? What I meant is that they left in the GA altitude, which would cause FLCH to engage as a climb, not a descent.
          Is this a joke? Here we go again.
          Why don't you read what I said, what MCM said, and what you hav ejust said above?

          NO. THE AP WITH THE FD IN FLCH DID NOT INITIATE A CLIMB BECAUSE THEY LEFT IN THE GA ALTITUDE. IT INITIATED A CLIMB BECAUSE THE SPEED WAS 20 KTS FASTER THAN THE SELECTED SPEED, SO IT PITCHED UP TO SLOW DOWN AND WOULD HAVE DONE SO EVEN IF THE SELECTED ALTITUDE WAS BELOW THE ACTUAL ALTITUDE AND WHATEVER THRUST WAS APPLIED. PITCH CONTROLS SPEED. SPEED ON ELEVATOR. THAT'S THE CORE OF FLCH.
          (Not shouting, just capitals are more visible and easier to read).

          What the AT did because the altitude was higher than actual was add thrust to sustain the climb (that had been initiated to slow down, not to gain altitude).

          If the selected altitude had been lower than the actual altitude, the airplane would have pitched up to slow down, but it would have not added thrust, and when slowed down to the selected airspeed it would have nosed down again to hold the speed.

          If the selected speed had been faster than the actual speed, then the airplane would have pitched down to speed up, regardless of what altitude was selected. If the selected altitude was higher, then after pitching down and achieving the selected speed, the AT would have added thrust to climb, and the FD/AT would have pitched up to hold the speed.

          --- 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 Evan View Post
            MCM, when you properly select FLCH, don't you also set proper values for speed and altitude? What I meant is that they left in the GA altitude, which would cause FLCH to engage as a climb, not a descent. I understand your point about being overwhelmed but it seems pretty ignorant to be 'pressing buttons' without setting the criteria that determine the AP's reaction to the selected mode. At least in the other instances I've read about where FLCH is abused for fast descent, the pilots knew that a lower altitude (like 0') was they key to doing this.
            What I could have done is:
            Selected FLCH and idle the throttles.
            The plane would have initially pitch up to slow down to the selected speed (Vapp) and then pitch down to hold that speed.
            With the throttles idled and the airplane fully dirty, this would have resulted in a fast descent rate.
            When the airplane approached the desired glide path, I would select VS (if no glide slope is available for the AP to follow), that would have made the AT to kick in again in speed hold mode, and adjusted the VS to some 750 fpm (an VS in pm of "half the speed in knots times ten" gives you a glide path of 3 degrees).
            And the selected altitude? You could have left it in 3000 and the above would have worked the same.
            I would have not done so, though. As a safety measure, I would have entered the minimum altitude where I would have gone around if I had not achieved a stabilized approach. That would give me an additional protection: If by that altitude the I didn't change the mode to VS, the plane by itself would switch to alt hold (AP) / speed hold (AT), so it would not keep descending and it would keep the speed.
            Oh, and I would have done all that much higher than they did. Like where the NTSB animation starts.

            --- 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
              Correct.


              Is this a joke? Here we go again.
              Why don't you read what I said, what MCM said, and what you hav ejust said above?

              NO. THE AP WITH THE FD IN FLCH DID NOT INITIATE A CLIMB BECAUSE THEY LEFT IN THE GA ALTITUDE. IT INITIATED A CLIMB BECAUSE THE SPEED WAS 20 KTS FASTER THAN THE SELECTED SPEED,
              YES, Gabriel. From the report:

              Because the MCP - selected altitude of 3,000 ft was above the airplane’s current altitude of abou t 1,550 ft msl (and in THR mode, the A/T applies thrust appropriate to attain the selected altitude), the thrust levers began to advance to initiate a climb.
              My point is this: if the PF had first entered a lower target altitude (say MDA or a bit above that) then he would have gotten IDLE thrust without touching the thrust levers and thereby without sending the A/T into HOLD. At the safe target altitude (if another mode has not been armed or selected, the AT would hae brought on thrust to maintain that altitude. Instead he got additional thrust (and pitch, due to the lower target speed) which exacerbated the above glideslope condition. That's how I understand FLCH anyway.

              This, I believe, is why he manually moved the thrust levers and dumped the automation. I don't think he was ever intending to hand fly the final.

              MCM believes he knew the functions of FLCH. I find it hard to concur when he is using it for descent without setting a descent altitude.

              Comment


              • Getcha popcorn !!!

                Comment


                • Yes, you should check the altitude and then press FLCH.

                  But the PF was overloaded!

                  I really, really don't think you understand the dynamic. Perhaps BB would be able to explain it better than I. He's pressed the button because he thought it would do what he wanted, without realising the altitude had been set above. Maybe the PM actually set it, and the PF didn't consciously realise. It happens.

                  When FLCH has been pressed and the thrust starts to come on, the PF correctly identifies that it is not doing what he wants it to do, and pulls the thrust to IDLE. FLCH recognises this, and then says "ok, if you want IDLE, I'll leave it there".

                  What SHOULD have happened next is that the autopilot AND auto throttle should have been disconnected as neither was doing as they desired. Sadly that didn't happen.

                  Comment


                  • Originally posted by MCM View Post
                    Yes, you should check the altitude and then press FLCH.

                    But the PF was overloaded!
                    MCM, The report does consider this:
                    The process of decelerating and configuring for landing would have been much easier, the pace of activities slower, and the workload less if it was not necessary for the PF and PM to both lose excess altitude and slow down after reaching the 5 nm point. Because they had to do both , they encountered a period of increased workload when they were engaged in parallel tasks for an extended period of time during a critical portion of the approach. This, in addition to the PF’s failure to make a callout when he selected FLCH SPD pitch mode on the MCP, reduced their ability to effectively crosscheck each other’s actions and monitor changes in the status of the autoflight system. The NTSB concludes that the flight crew ’s mismanagement of the airplane’s vertical profile during the initial approach led to a period of increased workload that reduced the PM’s awareness of the PF’s actions around the time of the unintended deactivation of automatic airspeed control.
                    Originally posted by MCM
                    He's pressed the button because he thought it would do what he wanted, without realising the altitude had been set above. Maybe the PM actually set it, and the PF didn't consciously realise. It happens.
                    The thing is, the PF set the MCP altitude himself (as the GA altitude) and made this callout just seconds prior to selecting FLCH (about 14 secs).
                    11:25:43.4
                    HOT - 2 (missed) approach three thousand * *
                    The PM was probably absorbed with watching the speed and getting to flaps 30 and didn't notice that the PF had made the MCP mode change. FLCH was only engaged for three seconds before the PF disconnected the AP.
                    Because the PM moved the flap lever to the flaps 30 position about 3 seconds after the PF selected FLCH SPD on the MCP, it is likely that at that time, the PM was monitoring the airspeed in preparation for changing the flap setting, which may have been why he missed the cues indicating the AFDS and A/T mode changes. At the same time as the PM selected flaps 30, the PF disconnected the A/P by double - clicking the wheel switch, which prevented the A/P disconnect aural alarm from sounding. The PF did not make the required “manual flight” callout when he disconnected the A/P. However, the disconnection of the A/P was apparently noticed by the PM because he called out “flight director,” indicating the change to the AFDS status displayed on the PFDs.
                    I guess I don't understand where to draw the line between 'overloaded' and 'incompetent', but, with all deference to you MCM as the professional voice of experience, it seems pretty obvious in my armchair point-of-view that the PF was not educated on the functionality of FLCH if he set a higher altitude and then seconds later selected the mode.

                    But in any case I don't see being overloaded as an excuse for throwing CRM out the window.

                    Comment


                    • Originally posted by Evan View Post
                      YES, Gabriel. From the report:

                      Because the MCP - selected altitude of 3,000 ft was above the airplane’s current altitude of abou t 1,550 ft msl (and in THR mode, the A/T applies thrust appropriate to attain the selected altitude), the thrust levers began to advance to initiate a climb.
                      My point is this: if the PF had first entered a lower target altitude (say MDA or a bit above that) then he would have gotten IDLE thrust without touching the thrust levers and thereby without sending the A/T into HOLD. At the safe target altitude (if another mode has not been armed or selected, the AT would hae brought on thrust to maintain that altitude. Instead he got additional thrust (and pitch, due to the lower target speed) which exacerbated the above glideslope condition. That's how I understand FLCH anyway.

                      This, I believe, is why he manually moved the thrust levers and dumped the automation. I don't think he was ever intending to hand fly the final.
                      Okay, I agree with all that. Just keep in mind that regardless of the selected altitude (even if it was lower or 0ft) the plane would have still initially pitched up (and start to climb or at least reduce the sink rate) to slow down because the selected speed was 20+ kts slower than the actual speed.

                      The difference, as you said, is that with a lower selected altitude the AT would have not added thrust.

                      But, as far as I understand the FLCH mode, if the selected altitude had been lower then it wouldn't have minded that the TL were idled by the AT or manually. Yes, the AT mode would have remained THR in the first case or changed to HLD in the second case. But upon reaching the selected altitude, the FD/AP would have changed to ALT HLD, the AT would have detected that the FD was not in a "pitch controls speed" anymore, and would have reverted to SPEED HLD, regardless of whether it was in THR or HLD at that time. The same would have happened if the pilot at any time changed the AP mode from FLCH to any other mode, say VS.

                      --- 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 MCM View Post
                        Yes, you should check the altitude and then press FLCH.

                        But the PF was overloaded!

                        I really, really don't think you understand the dynamic. Perhaps BB would be able to explain it better than I. He's pressed the button because he thought it would do what he wanted, without realising the altitude had been set above. Maybe the PM actually set it, and the PF didn't consciously realise. It happens.

                        When FLCH has been pressed and the thrust starts to come on, the PF correctly identifies that it is not doing what he wants it to do, and pulls the thrust to IDLE. FLCH recognises this, and then says "ok, if you want IDLE, I'll leave it there".

                        What SHOULD have happened next is that the autopilot AND auto throttle should have been disconnected as neither was doing as they desired. Sadly that didn't happen.
                        MCM, I see what you mean and concur.

                        What I don't understand is:
                        - Why did the PF rely on the AT to hold the speed if he had selected FLCH?
                        - Why did all three relay that the speed would be held by something or someone, and none of checked the speed for several seconds, basically between 500ft and 2 seconds before the impact?

                        --- 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 Evan View Post
                          But in any case I don't see being overloaded as an excuse for throwing CRM out the window.
                          CRM was obviously a strong issue here.

                          But the individual actions of the PF too.

                          --- 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


                          • Gabriel - Because he was overloaded!

                            You guys are ignoring the significant effects of overload on performance.

                            The pilot did not
                            consciously
                            select FLCH. If he was thinking rationally, he would never have used that mode. He was reacting - trying something, without clear thought. It was a method he would have used, and seen used for other approaches, and without clear brainspace, he defaulted to doing it.

                            That does not mean he doesn't understand the significance of the mode, or how it operates when you sit him down and ask him - or even when it is being used in situations when he is 'ahead of the aircraft'. But he was clearly uncomfortable in the scenario, and didn't have the tools needed to get himself out of it. That comes into the realms of training.

                            Strange things happen during overload. Task fixation increases. Your hearing goes. You say things automatically. A great example is the question 'have we done the landing checklist yet?' or 'Has he cleared us to land?'. These are questions that alert you to task saturation. You can, and do, do things 'automatically' without rational thought. Pretty much every pilot can tell you of a time that they've done a checklist 'in autopilot', and then afterwards gone 'hang on, I didn't actually check any of those items'. Its classic overload.

                            As is not hearing input from the other pilot (how many times have we seen F/O's telling Captains that they should be going around, but the Captain really isn't hearing them? It isn't the Captain being bolshy, its the Captain not hearing what they're saying. As is using modes that aren't appropriate. Even if the PF didn't know the use of FLCH (which I believe he did), the PM sure as hell did. The PF wasn't flying the aircraft, and the PM wasn't monitoring him.

                            Yes, training is absolutely part of this. A well trained crew is far less likely to get into an overload scenario. But it isn't because FLCH is 'tricky', its bloody easy. Its a BASIC auto flight mode that we revert to when the more 'managed' modes aren't appropriate. Very simple, does what it says on the tin.

                            Comment


                            • Originally posted by MCM View Post
                              Gabriel - Because he was overloaded!

                              You guys are ignoring the significant effects of overload on performance.

                              The pilot did not select FLCH. If he was thinking rationally, he would never have used that mode. He was reacting - trying something, without clear thought. It was a method he would have used, and seen used for other approaches, and without clear brainspace, he defaulted to doing it.

                              That does not mean he doesn't understand the significance of the mode, or how it operates when you sit him down and ask him - or even when it is being used in situations when he is 'ahead of the aircraft'.
                              MCM, you are wrong by the own confession of the PF in the post-accident interview. Basically, he didn't understand a thing of how the system works.

                              Originally posted by NTSB final report
                              The PF stated that the 777 A/T system would always maintain the selected airspeed as
                              long as the A/T was on. He said that if a pilot overrode the thrust levers manually, the A/T would
                              resume controlling airspeed when the pilot released the thrust levers. He stated that it was
                              irrelevant whether he had pushed the FLCH button immediately before disconnecting the A/P
                              during the accident approach because he was in manual flight and the A/T was always working.
                              He thought the A/T should have automatically advanced the thrust levers upon reaching the
                              MCP-selected airspeed during the accident approach, and he did not understand why that did not
                              occur. Furthermore, he thought the A/T system should have automatically transitioned to TO/GA
                              when the airplane reached minimum airspeed.

                              --- 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
                                MCM, you are wrong by the own confession of the PF in the post-accident interview. Basically, he didn't understand a thing of how the system work.
                                Maybe he was still panicking.

                                Read that section carefully. It becomes obvious that that Asiana ground school instructors were quite clueless of this A/T-modal interaction as well, attributing the lack of A/T function to 'an anomaly' in the B777 systems. Why Boeing hadn't made this more clear to them is a big question.

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