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  • #61
    I can see density altitude having three effects:
    • Ground speed, for a given IAS will be higher. If the a/c is flying an approach at a fixed angle (as when using an ILS) as opposed to fixed vertical speed, that means v/s will be higher too.
    • Engine thrust will be lower.
    • I'd think the engines would spool more slowly in less dense air. That's just a guess on my part, but the turbo on my car spools considerably faster in cold weather than when it's hot...

    So maybe each one of the above isn't enough to make a big difference in the ability to initiate a go-around, but together they do?
    Be alert! America needs more lerts.

    Eric Law

    Comment


    • #62
      Originally posted by BoeingBobby View Post
      Even at sea level, at those temps, more like 115 when I was in Bahrain last week, it comes into play. WINDSHEAR, NO configuration changes until you are up, away, and have stable airspeed.
      Well, Gabriel says it's not an issue, so don't worry about it.

      Comment


      • #63
        Originally posted by ATLcrew View Post
        Well, Gabriel says it's not an issue, so don't worry about it.
        Well, hell, another gosh-darn gray area we can argue about all day long...Please tell us your opinion.

        The Tommy Jock should be aware that on a cold day, full tanks and two full sized males, he can sometimes achieve 500 FPM climbs, that cannot be achieved on hazy hot summer afternoons.

        On the other hand, you guys who drive big powerful jets should not have any problem at all whatsoever establishing a climb on a hot day at 3500 feet density altitude...a climb that still blows away a lightly loaded 172S on a cold day.

        My bottom line comment is, "don't tell me the damn plane couldn't climb", but maybe you and BB are saying that "it takes a few more seconds to get the descent turned around as compared to how it works in Ancorage"....

        Yes/No/Maybe?

        Thanks, as always.
        Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

        Comment


        • #64
          Originally posted by elaw View Post
          I can see density altitude having three effects:
          • Ground speed, for a given IAS will be higher. If the a/c is flying an approach at a fixed angle (as when using an ILS) as opposed to fixed vertical speed, that means v/s will be higher too.
          • Engine thrust will be lower.
          • I'd think the engines would spool more slowly in less dense air. That's just a guess on my part, but the turbo on my car spools considerably faster in cold weather than when it's hot...

          So maybe each one of the above isn't enough to make a big difference in the ability to initiate a go-around, but together they do?
          - Ground speed (and vertical speed at constant angle) will be about 5% faster at these density altitude. Not a significant difference.
          - TOGA thrust may be lower (depending on whether the engine is flat rated and by how much), but this should not be a problem because you don't need thrust to initially arrest the descent and because you need way less than TOGA to sustain a climb. The stabilized climb rate would be smaller but that has nothing to do neither with the ability to avoid ground contact nor with the fact that they did that with the gear up (if that's what happened and not a gear collapse).
          - Same for an eventual slower spool up.

          --- 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


          • #65
            Originally posted by ATLcrew View Post
            Well, Gabriel says it's not an issue, so don't worry about it.
            Pay attention to what I am saying. Make a difference in what?

            In whether the plane contacts the ground before arresting the descent, or after doing so trading airspeed only to descend again? 5000 ft of density altitude will have a small impact in performance, but 1ft of altitude can make the difference between ground contact or just a close low pass.

            In whether such eventual ground contact is done withe the gear down and locked or with gear unsafe / in transit / up? No, density altitude cannot make a difference.

            As BB said, positive climb, stable (or increasing) airspeed, and only then gear up. This will guarantee either no ground contact or that the gear is down if there is ground contact (i.e. will guarantee no gear up ground contact regardless of the density altitude)

            --- 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


            • #66
              Originally posted by Gabriel View Post
              ...Make a difference in what?...
              In whether a crew runs what seems to be a well-functioning airplane into the ground or not...

              Again, it's outsider, gray-area, BS-Aggie thinking versus black and white scientific aeroengineer thinking.

              Yeah, the procedure (fundamental or rote regurgitated) was not followed..."we" get that...procedure is important even if you consider fundamentals important.

              But, procedure was not_followed...

              ...so, what did the poor, (albeit well-trained, intelligent, said-to-be-great-pilots***see footnote***) human beings do or THINK they were doing.

              Okay...power up, looking good [Looking good improperly used instead of the correct "positive rate"], gear up, flaps 15...wow, this thing's sagging a bit... I can see Density Altitude (even though it's a sea-level airport) rearing it's ugly little head here...just like it does in a 172...just doesn't climb as crisply at 90 degrees, even though Flyover America's only 600 ft MSL...

              This is nothing but pure ass-hat speculation- but is inline with the question, "Why did they run a well functioning rather expensive airplane into the ground, and risk burning up everyone's carry on?".

              ***Footnote***Pilots who bend airplanes are generally well-trained, intelligent and respected.
              Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

              Comment


              • #67
                Originally posted by 3WE View Post

                Yeah, the procedure (fundamental or rote regurgitated) was not followed..."
                You know something we don't?

                As far as we know the gear could have been down and locked, windshear could have won the battle and this thing could have been slammed into a gear-collapsing impact with the runway. If you don't think it hit hard enough to do that, have a look at the #2 engine.

                Density altitude might have played a contributing role but there's no way that alone is going to prevent a go-around. If there was a lack of thrust it probably had more to do with a lack of thrust command.

                But then again... remember the BA 777 crash... That investigation revealed three seperate momentary loss of thrust incidents. All Trent 895's. This one had Trent 892's. Is there still a vulnerability here?

                * Now that I've read two seperate pax reports of a single hard touchdown, I'm withdrawing my flight/ground mode issue speculations.

                Comment


                • #68
                  Originally posted by Evan View Post
                  ...You know something we don't?...
                  Only that as "we" wait for the final report, the theory that the gear was improperly and prematurely raised seems to be a prime topic for ass-hat parlour speculation.
                  Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                  Comment


                  • #69
                    Originally posted by 3WE View Post
                    Well, hell, another gosh-darn gray area we can argue about all day long...Please tell us your opinion.
                    Well, I was going to, but Gabriel said not to worry about it, so I'll just let it ride.

                    Comment


                    • #70
                      Originally posted by ATLcrew View Post
                      Well, I was going to, but Gabriel said not to worry about it, so I'll just let it ride.
                      This was on our company website this morning:

                      The crash of an Emirates B777 during an attempted go-around in Dubai last Wednesday was always an accident waiting to happen.
                      It was not the fault of the pilots, the airline or Boeing, because this accident could have happened to any pilot in any airline flying any modern glass cockpit airliner — Airbus, Boeing or Bombardier — or a large corporate jet with autothrottle.
                      It is the result of the imperfect interaction of the pilots with supposedly failsafe automatics, which pilots are rigorously trained to trust, which in this case failed them.
                      First, let us be clear about the effect of hot weather on the day. All twin-engine jet aircraft are certified at maximum takeoff weight to climb away on one engine after engine failure on takeoff at the maximum flight envelope operating temperature — 50 degrees C in the case of a B777 — to reach a regulatory climb gradient minimum of 2.4 per cent.
                      The Emirates B777-300 was operating on two engines and at a lower landing weight, so climb performance should not have been a problem. I have operated for years out of Dubai in summer, where the temperature is often in the high 40s, in both widebody Airbus and Boeing B777 aircraft.
                      Secondly, a pilot colleague observed exactly what happened as he was there, waiting in his aircraft to cross runway 12L. The B777 bounced and began a go-around. The aircraft reached about 150 feet (45 metres) with its landing gear retracting, then began to sink to the runway.
                      This suggests that the pilots had initiated a go-around as they had been trained to do and had practised hundreds of times in simulators, but the engines failed to respond in time to the pilot-commanded thrust. Why?
                      Bounces are not uncommon. They happen to all pilots occasionally. What was different with the Emirates B777 bounce was that the pilot elected to go around. This should not have been a problem as pilots are trained to apply power, pitch up (raise the nose) and climb away. However pilots are not really trained for go-arounds after a bounce; we practise go-arounds from a low approach attitude.
                      Modern jets have autothrottles as part of the autoflight system. They have small TOGA (take off/go-around) switches on the throttle levers they click to command autothrottles to control the engines, to deliver the required thrust. Pilots do not physically push up the levers by themselves but trust the autothrottles to do that, although it is common to rest your hand on the top of the levers. So, on a go-around, all the pilot does is click the TOGA switches, pull back on the control column to raise the nose and — when the other pilot, after observing positive climb, announces it — calls “gear up” and away we go!
                      But in the Dubai case, because the wheels had touched the runway, the landing gear sensors told the autoflight system computers that the aircraft was landed. So when the pilot clicked TOGA, the computers — without him initially realising it — inhibited TOGA as part of their design protocols and refused to spool up the engines as the pilot commanded.
                      Imagine the situation. One pilot, exactly as he has been trained, clicks TOGA and concentrates momentarily on his pilot’s flying display (PFD) to raise the nose of the aircraft to the required go-around attitude — not realising his command for TOGA thrust has been ignored. The other pilot is concentrating on his PFD altimeter to confirm that the aircraft is climbing due to the aircraft momentum. Both suddenly realise the engines are still at idle, as they had been since the autothrottles retarded them at approximately 30 feet during the landing flare. There is a shock of realisation and frantic manual pushing of levers to override the autothrottle pressure.
                      But too late. The big engines take seconds to deliver the required thrust before and before that is achieved the aircraft sinks to the runway.
                      It could have happened to any pilot caught out by an unusual, time-critical event, for which rigorous simulator training had not prepared him.
                      Automation problems leading to pilot confusion are not uncommon; but the designers of the autoflight system protocols should have anticipated this one. Perhaps an audible warning like “manual override required” to alert the pilots immediately of the “automation disconnect”.
                      My feeling is the pilots were deceived initially by the autothrottle refusal to spool up the engines, due to the landing inhibits, and a very high standard of simulator training by which pilots are almost brainwashed to totally rely on the automatics as the correct thing.

                      Comment


                      • #71
                        This is why I prefer to at least START my GAs in fully manual mode. No need to worry about what the automation might or might not do, if you're not using any. And yes, Evan, that, too, is an approved procedure.

                        Comment


                        • #72
                          Originally posted by ATLcrew View Post
                          This is why I prefer to at least START my GAs in fully manual mode. No need to worry about what the automation might or might not do, if you're not using any. And yes, Evan, that, too, is an approved procedure.

                          My thoughts and personal procedure as well!

                          Comment


                          • #73
                            Originally posted by BoeingBobby View Post
                            This was on our company website this morning:

                            The crash of an Emirates B777 during an attempted go-around in Dubai last Wednesday was always an accident waiting to happen.
                            It was not the fault of the pilots, the airline or Boeing, because this accident could have happened to any pilot in any airline flying any modern glass cockpit airliner — Airbus, Boeing or Bombardier — or a large corporate jet with autothrottle.
                            It is the result of the imperfect interaction of the pilots with supposedly failsafe automatics, which pilots are rigorously trained to trust, which in this case failed them.
                            First, let us be clear about the effect of hot weather on the day. All twin-engine jet aircraft are certified at maximum takeoff weight to climb away on one engine after engine failure on takeoff at the maximum flight envelope operating temperature — 50 degrees C in the case of a B777 — to reach a regulatory climb gradient minimum of 2.4 per cent.
                            The Emirates B777-300 was operating on two engines and at a lower landing weight, so climb performance should not have been a problem. I have operated for years out of Dubai in summer, where the temperature is often in the high 40s, in both widebody Airbus and Boeing B777 aircraft.
                            Secondly, a pilot colleague observed exactly what happened as he was there, waiting in his aircraft to cross runway 12L. The B777 bounced and began a go-around. The aircraft reached about 150 feet (45 metres) with its landing gear retracting, then began to sink to the runway.
                            This suggests that the pilots had initiated a go-around as they had been trained to do and had practised hundreds of times in simulators, but the engines failed to respond in time to the pilot-commanded thrust. Why?
                            Bounces are not uncommon. They happen to all pilots occasionally. What was different with the Emirates B777 bounce was that the pilot elected to go around. This should not have been a problem as pilots are trained to apply power, pitch up (raise the nose) and climb away. However pilots are not really trained for go-arounds after a bounce; we practise go-arounds from a low approach attitude.
                            Modern jets have autothrottles as part of the autoflight system. They have small TOGA (take off/go-around) switches on the throttle levers they click to command autothrottles to control the engines, to deliver the required thrust. Pilots do not physically push up the levers by themselves but trust the autothrottles to do that, although it is common to rest your hand on the top of the levers. So, on a go-around, all the pilot does is click the TOGA switches, pull back on the control column to raise the nose and — when the other pilot, after observing positive climb, announces it — calls “gear up” and away we go!
                            But in the Dubai case, because the wheels had touched the runway, the landing gear sensors told the autoflight system computers that the aircraft was landed. So when the pilot clicked TOGA, the computers — without him initially realising it — inhibited TOGA as part of their design protocols and refused to spool up the engines as the pilot commanded.
                            Imagine the situation. One pilot, exactly as he has been trained, clicks TOGA and concentrates momentarily on his pilot’s flying display (PFD) to raise the nose of the aircraft to the required go-around attitude — not realising his command for TOGA thrust has been ignored. The other pilot is concentrating on his PFD altimeter to confirm that the aircraft is climbing due to the aircraft momentum. Both suddenly realise the engines are still at idle, as they had been since the autothrottles retarded them at approximately 30 feet during the landing flare. There is a shock of realisation and frantic manual pushing of levers to override the autothrottle pressure.
                            But too late. The big engines take seconds to deliver the required thrust before and before that is achieved the aircraft sinks to the runway.
                            It could have happened to any pilot caught out by an unusual, time-critical event, for which rigorous simulator training had not prepared him.
                            Automation problems leading to pilot confusion are not uncommon; but the designers of the autoflight system protocols should have anticipated this one. Perhaps an audible warning like “manual override required” to alert the pilots immediately of the “automation disconnect”.
                            My feeling is the pilots were deceived initially by the autothrottle refusal to spool up the engines, due to the landing inhibits, and a very high standard of simulator training by which pilots are almost brainwashed to totally rely on the automatics as the correct thing.
                            and if this "professional speculation" is correct, it will be one more strike against automation.

                            can't wait to hear evan scream and shout that despite a professional pilot opining that no one is really to blame, the airline and regulators are to blame for failing to train pilots in boeing aricraft how to do a proper go around in a semi-automated ac after a bounce....

                            Comment


                            • #74
                              Originally posted by BoeingBobby View Post
                              This was on our company website this morning:

                              The crash of an Emirates B777 during an attempted go-around in Dubai last Wednesday was always an accident waiting to happen.
                              It was not the fault of the pilots, the airline or Boeing, because this accident could have happened to any pilot in any airline flying any modern glass cockpit airliner — Airbus, Boeing or Bombardier — or a large corporate jet with autothrottle.
                              It is the result of the imperfect interaction of the pilots with supposedly failsafe automatics, which pilots are rigorously trained to trust, which in this case failed them.
                              First, let us be clear about the effect of hot weather on the day. All twin-engine jet aircraft are certified at maximum takeoff weight to climb away on one engine after engine failure on takeoff at the maximum flight envelope operating temperature — 50 degrees C in the case of a B777 — to reach a regulatory climb gradient minimum of 2.4 per cent.
                              The Emirates B777-300 was operating on two engines and at a lower landing weight, so climb performance should not have been a problem. I have operated for years out of Dubai in summer, where the temperature is often in the high 40s, in both widebody Airbus and Boeing B777 aircraft.
                              Secondly, a pilot colleague observed exactly what happened as he was there, waiting in his aircraft to cross runway 12L. The B777 bounced and began a go-around. The aircraft reached about 150 feet (45 metres) with its landing gear retracting, then began to sink to the runway.
                              This suggests that the pilots had initiated a go-around as they had been trained to do and had practised hundreds of times in simulators, but the engines failed to respond in time to the pilot-commanded thrust. Why?
                              Bounces are not uncommon. They happen to all pilots occasionally. What was different with the Emirates B777 bounce was that the pilot elected to go around. This should not have been a problem as pilots are trained to apply power, pitch up (raise the nose) and climb away. However pilots are not really trained for go-arounds after a bounce; we practise go-arounds from a low approach attitude.
                              Modern jets have autothrottles as part of the autoflight system. They have small TOGA (take off/go-around) switches on the throttle levers they click to command autothrottles to control the engines, to deliver the required thrust. Pilots do not physically push up the levers by themselves but trust the autothrottles to do that, although it is common to rest your hand on the top of the levers. So, on a go-around, all the pilot does is click the TOGA switches, pull back on the control column to raise the nose and — when the other pilot, after observing positive climb, announces it — calls “gear up” and away we go!
                              But in the Dubai case, because the wheels had touched the runway, the landing gear sensors told the autoflight system computers that the aircraft was landed. So when the pilot clicked TOGA, the computers — without him initially realising it — inhibited TOGA as part of their design protocols and refused to spool up the engines as the pilot commanded.
                              Imagine the situation. One pilot, exactly as he has been trained, clicks TOGA and concentrates momentarily on his pilot’s flying display (PFD) to raise the nose of the aircraft to the required go-around attitude — not realising his command for TOGA thrust has been ignored. The other pilot is concentrating on his PFD altimeter to confirm that the aircraft is climbing due to the aircraft momentum. Both suddenly realise the engines are still at idle, as they had been since the autothrottles retarded them at approximately 30 feet during the landing flare. There is a shock of realisation and frantic manual pushing of levers to override the autothrottle pressure.
                              But too late. The big engines take seconds to deliver the required thrust before and before that is achieved the aircraft sinks to the runway.
                              It could have happened to any pilot caught out by an unusual, time-critical event, for which rigorous simulator training had not prepared him.
                              Automation problems leading to pilot confusion are not uncommon; but the designers of the autoflight system protocols should have anticipated this one. Perhaps an audible warning like “manual override required” to alert the pilots immediately of the “automation disconnect”.
                              My feeling is the pilots were deceived initially by the autothrottle refusal to spool up the engines, due to the landing inhibits, and a very high standard of simulator training by which pilots are almost brainwashed to totally rely on the automatics as the correct thing.
                              OK, hold on a sec. FIrst of all, if this witness account is accurate, I re-submit my original theory which is exactly this one.

                              But there are problems with this. For one thing, two passengers have reported that everything was normal until the plane hit the ground very hard and slid down the runway. That doesn't sound like a bounce to me. There have been no pax reports of a bounce.

                              Secondly, I know Boeing uses a multi-second delay after touchdown on the 747 before the idle mode switches from approach (flight) to minimum (ground) idle. They do this EXACTLY to allow a safe GA after touchdown. It stands to reason that they would also provide this delay before inhibiting the TO/GA switches on the 777—for the same reason. But this I don't know.

                              Because ground mode is activated by main gear beam angle, I also think you need not only ground contact but derotation beyond what is common in a bounce. Maybe not.

                              In any event, let's be clear about one thing:

                              it is common to rest your hand on the top of the levers.
                              No, it is procedure to rest your hands on the thrust levers during critical phases. For exactly this reason. The TO/GA switches are a tool (as is the autothrottle). If they don't work, it is your job to monitor that (by feel) and set thrust manually. If we have 7000+ hour pilots out there flying 777's who can't keep a hand on the thrust levers... Oh, right... Ho Lee Fuk...

                              It is also procedure for the PM to verify GA thrust. So did both pilots blip out here?

                              If this turns out to be the case, the fallout better be an industry-wide re-education on the absolute necessity of that hand on the thrust levers during critical phases of autothrottle operation.... this is so basic...

                              EDIT: I've since seen one pax video claiming the plane came down "normally", then ascended before hitting the runway. Nothing about an actual touchdown before ascending but...

                              Comment


                              • #75
                                Originally posted by BoeingBobby View Post
                                This was on our company website this morning:

                                If/Then...however...in that case...do this...except when that.
                                Originally posted by AirbusWorshipper (and BB)

                                I prefer to throttle up, pull up, monitor instruments, et al. using my hands, eyes and fundamental concepts as well as the memory checklist
                                I like it (not that it's my place to render judgement).
                                Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                                Comment

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