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Pakistan plane crash: Jet carrying 107 people crashes into houses near airport

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  • Originally posted by Evan View Post

    Indeed, but we are dealing with crazy here. It would seem to me, if I place no value on safety (or the heightened possibility of a missed approach), that the most cost-efficient alternative (remember, the target is the best CI, a compromise between fuel conservation and operating time) would be to cover more distance in less time at cruise where the engines are most efficient and then to do the entire descent including most of the final 3nm at idle while having minimum drag out for as long as possible. Would you agree?
    No, I wouldn't.

    I don't think that the airline was counting with the 3-minutes reduction in the turnaround time as to squeeze another flight in the day, nor that repeated 3-minutes savings throughout the day would be enough to squeeze in another flight. At the same time, I don't think that the crew would make any less money for saving 3 minutes of flight, otherwise it would be an incentive to make the flight last more, not less. So with all that, the differential cost of operating time is about zero.

    Additionally, the flight profile they flew doesn't seem to be the one you would if you wanted to minimize time, which is extend cruise as much as possible then idle and full flight speedbrakes fully extended to Vmo down to 10000 ft, level off still with speedbrakes and idle, slow down to 250kts, continue descent with 250 kts, speedbrakes and idle until about 2500ft ARL and 10 miles out, then level off and extend landing gear and slats flaps as soon as speed allows (you are still at idle and with the speedbrakes extended for as long as the combination of speedbrakes and flaps setting is legal) and intercept the glide slope while doing so, arriving at final approach speed when you are at about 1500 ft, then retract spoilers (if still extended) and add approach thrust to stabilize the approach and do the before landing checklist finalizing just before the 1000 ft gate.

    This is not only the fastest descent/approach but also a very fuel-saving one, although not as much as gliding from as far as possible which was the previous one I mentioned.

    --- 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

      No, I wouldn't.

      I don't think that the airline was counting with the 3-minutes reduction in the turnaround time as to squeeze another flight in the day, nor that repeated 3-minutes savings throughout the day would be enough to squeeze in another flight. At the same time, I don't think that the crew would make any less money for saving 3 minutes of flight, otherwise it would be an incentive to make the flight last more, not less. So with all that, the differential cost of operating time is about zero.

      Additionally, the flight profile they flew doesn't seem to be the one you would if you wanted to minimize time, which is extend cruise as much as possible then idle and full flight speedbrakes fully extended to Vmo down to 10000 ft, level off still with speedbrakes and idle, slow down to 250kts, continue descent with 250 kts, speedbrakes and idle until about 2500ft ARL and 10 miles out, then level off and extend landing gear and slats flaps as soon as speed allows (you are still at idle and with the speedbrakes extended for as long as the combination of speedbrakes and flaps setting is legal) and intercept the glide slope while doing so, arriving at final approach speed when you are at about 1500 ft, then retract spoilers (if still extended) and add approach thrust to stabilize the approach and do the before landing checklist finalizing just before the 1000 ft gate.

      This is not only the fastest descent/approach but also a very fuel-saving one, although not as much as gliding from as far as possible which was the previous one I mentioned.
      Again, I see everything you are saying but I don't think you see what I am getting at.

      Firstly, the issue of operating time isn't about turnaround, it's about costs associated with operation including maintenance intervals and depreciable wear and tear. And I'm seeing around 8-12 minutes of operating time shaved off here. Multiply that by hundreds of flights a year. From a dirt cheap operator perspective.

      But, as far as technique is concerned, I'm speculating that a pressured directive from on high might have led a pilot with an imperfect understanding of everything you stated above to recklessly improvise a technique. What he tried to pull off here is essentially what I described above: prolonged flight at cruise, then a steep idle (OP DES) drop to join the glideslope from above about halfway down it (at about 5nm, not 10nm) with flaps first coming out less than 6nm out and landing flaps coming out at 3nm. So more distance covered at cruise, the remainder flown on energy alone and half the normal distance of the final flown with drag out. Screw the placard speeds (please, he's done this a million times and nothing's fallen off) and there's always enough runway needed to stop despite the higher landing speed.

      Dumb, yes. Crazy, indeed. Dangerous, or course. Diabolical, quite. But what if he'd pulled this off dozens of times? And what if management had rewarded him for his fuel conservation and flight time? It might start to look pretty smart.

      The real danger lurked in what was missing. Stability. Checklist procedures. CRM. So on day zero speed got away from him, workload got compressed, things got skipped, confused or overlooked (like overspeed warnings and gear warnings), he failed to configure the gear and there was no redundancy to contend with these errors, zero margin for error.

      That's becoming my theory for what it's worth.

      Comment


      • Originally posted by Evan View Post
        Firstly, the issue of operating time isn't about turnaround, it's about costs associated with operation including maintenance intervals and depreciable wear and tear.
        Meh, most of that in pressurized transport category planes is defined by cycle and hours. When you use the plane mostly for short flights like PIA does the flight cycles limit is reached first so the hours don't matter much.

        And I'm seeing around 8-12 minutes of operating time shaved off here.
        How so? I see 3 minutes at most. Don't confuse how short was the descent/approach with how much time they saved, because they made the descent shorter by making it steeper which means that they flew MORE time at cruise.

        then a steep idle (OP DES) drop
        It is the 2nd or 3rd time that you mention this. Do you have anything against and idle descent in open descent mode (i.e. speed-on-pitch)? For me it is the correct way to descend if not using VNAV.

        Dumb, yes. Crazy, indeed. Dangerous, or course. Diabolical, quite. But what if he'd pulled this off dozens of times? And what if management had rewarded him for his fuel conservation and flight time? It might start to look pretty smart.
        HE was management. Hence why the Smartwings incident reminded me of this PIA one.

        I am with you that he likely attempted some improvised fuel/time saving profile. But I don't think that the profile they ended up flying was what he had in mind. For example, I don't think that he intended to cross the threshold at 210 knots. I think they screwed it up even by their standards, and then were stubborn and arrogant to fix it in a proper way and instead attempted to salvage it. And they would have gotten away with it if it wasn't for the mysterious reason that they retracted the landing gear.

        --- 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
          It is the 2nd or 3rd time that you mention this. Do you have anything against and idle descent in open descent mode (i.e. speed-on-pitch)? For me it is the correct way to descend if not using VNAV.
          I only mentioned it because it parks the thrust at idle until a new mode transition. I do, however, have something against using it below 10,000 AGL, or at least below 5000 AGL. It's inherently vulnerable to pilot error and extremely dangerous at low altitude if the FCU is not set up correctly, as we have seen. And it shouldn't be needed there.

          I am with you that he likely attempted some improvised fuel/time saving profile. But I don't think that the profile they ended up flying was what he had in mind. For example, I don't think that he intended to cross the threshold at 210 knots. I think they screwed it up even by their standards, and then were stubborn and arrogant to fix it in a proper way and instead attempted to salvage it. And they would have gotten away with it if it wasn't for the mysterious reason that they retracted the landing gear.
          Yes, as I said, things went wrong this time.

          Comment


          • Originally posted by Evan View Post
            I do, however, have something against using it below 10,000 AGL, or at least below 5000 AGL. It's inherently vulnerable to pilot error and extremely dangerous at low altitude if the FCU is not set up correctly, as we have seen. And it shouldn't be needed there.
            I don't understand what you have in mind. What is the risk? If you could go from TOD all the way down to glideslope-intercept altitude without interruptions (something that you almost never can do due to ATC), I would leave it in open descent all the way to that point. Of course, when you level off at that altitude, or at any point in between due to ATC constrains, you would go to altitude hold and speed-on-thrust.

            And, by the way, I don't know how it works in the Airbus where the thrust levers are normally left in CLB unitl 20ft, but in the Boeing when you select what I think is called LVL CHG (IAS/MACH altitude mode in the MD-80) the thrust levers just stop being managed and they will stay put wherever you put them. You can put them in idle but if you want a lower sink rate you can move them forward a bit to add some thrust, and the pitch will adjust itself to keep the selected IAS/Mach.

            --- 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

              Where? Post # please?

              Why do you insist with just the gear issue? They crossed the threshold at 210kts overspeeding the flaps. CLEARLY and UNDOUBTEDLY (yes black and white) the gear was not the ony issue here. Even if they had lowered the gear and gotten away with it, this would have been very very VERY bad airmanship worth of immediately firing both pilots and revoking their licenses for life (again, yes, black and white) (although that would have never happened because no one outside of the airline would have know it and the airline was encouraging this behavior).
              I don't know- keep looking.

              And don't imply things he didn't say.

              I am paraphrasing, but my recollection is that he said he probably could have gotten the plane down and stabilized and configured and basically on-target for a normal landing...

              It would be a little challenging, but he thought he could do it if 10 cell phone batteries simultaneously caught fire [hint] and the closest airport was a similar situation.

              That being said, I think his first choice was to make a 360 (assuming the cell phone battery fires were extinguished).

              I don't think I'm saying it's JUST a gear issue.

              But I think Evan wants to write extensive descent procedures, and why would he expect THEM to be followed when "Gear-Down-Three-Green" seemed to escape this crew...

              And if they had remembered that equally basic (and liberally checklisted) procedure, the bad touch down and bad go-around would have extremely likely given them a powered aircraft...

              So, I do rank the gear screw up as kind of pivotal...

              Crossing the threshold at 210 knots does not guarantee a crash...and probably is OK on a 14K ft runway too. No wheelies....not so good.



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

              Comment


              • My point, again and for the last time, is that this was going to end bad sooner or later, gear up, overrun, landing gear collapse, loss of control or something. They had already had repeated incidents this year associated with this kind of hasty approaches.

                --- 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
                  My point, again and for the last time ...They had already had repeated incidents this year associated with this kind of hasty approaches.
                  Good. And, for this case, had they ‘put’ the gear down, no crash, regardless of “your point”.

                  The problem is not the steep approach.

                  I’ll give you:

                  1. Forgetting the gear.
                  2. Crossing the threshold at 200+ knots.
                  3. Dudes with fake pilots licenses being widespread.

                  Indeed,#3 could be said to be “an accident waiting to happen”, and might be grounds for more oversight and public beatings.

                  Your point also does not change the fact that someone might chop the power, use draggy things (like proper use of landing gear) and a little airmanship and maybe arrive at the runway in decent shape...
                  Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                  Comment


                  • Originally posted by 3WE View Post

                    Good. And, for this case, had they ‘put’ the gear down, no crash, regardless of “your point”.

                    The problem is not the steep approach.

                    I’ll give you:

                    1. Forgetting the gear.
                    2. Crossing the threshold at 200+ knots.
                    3. Dudes with fake pilots licenses being widespread.

                    Indeed,#3 could be said to be “an accident waiting to happen”, and might be grounds for more oversight and public beatings.

                    Your point also does not change the fact that someone might chop the power, use draggy things (like proper use of landing gear) and a little airmanship and maybe arrive at the runway in decent shape...
                    Man, are you serious or just trolling? As I said earlier, aviation safety is not about what you can't pull off on a good day, it's about defending against what can go wrong on a bad one. And sooner or later that bad day will arrive. This crash might be a perfect demonstration of that fact.

                    The following is true of all pilot error crashes:

                    And, for this case, had they____________, no crash.
                    For many of them, this also:

                    Had they not improvised themselves into a situation conducive to error, no crash.

                    Comment


                    • Originally posted by 3WE View Post
                      Your point also does not change the fact that someone might chop the power, use draggy things (like proper use of landing gear) and a little airmanship and maybe arrive at the runway in decent shape...
                      Be my guest.

                      But if the plan fails and you are not stabilized by 500ft (which includes being in lading configuration, on track, on slope, on speed and landing checklist complete), go around.

                      --- 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


                      • Ok Evan, you win. If they had made a conservative descent and forgotten the gear, they would not have crashed.
                        Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                        Comment


                        • Originally posted by 3WE View Post
                          Ok Evan, you win. If they had made a conservative descent and forgotten the gear, they would not have crashed.
                          If they had done a conservative approach and used stabilized approach criteria they would have been much more unlikely to raise he gear after lowering it and not notice or ignore the warnings. For once, they would not have had other GPWS warnings like sink rate and pull up, only too low gear, and they would not have had the flaps overspend warning. And then, they would have had much less workload and would have followed a more standard flow of actions that would have reduced the likelihood of the mistake in the first place.

                          AND if they still landed with the gear up, they would have been much less likely to initiate a go around. You'll see, they didn't initiate the go around the second they touched down on the engines. They bounced at least 3 times barely losing speed in the process. They were too fast and overspending the flaps, so lots of lift still and little weight-on-engines and hence little friction. Now, combine touching down way too far down the runway, way too fast, and not slowing down. Compare with crossing the threshold at 35 ft and Vref, retarding, flaring and bleeding off some speed before touching down (still on the engines) in the first 2000 ft of the runway with 30 knots less of speed. They would have not bounced. The plane would have firmly settled on the runway. Starting the landing roll with much less speed, no bounces, much more friction, decelerating fairly and with a whole runway ahead would have reduced a lot of motivation to attempt the go-around. And even if they tried, at that low speed it would have likely been impossible to achieve the high AoA required to make lift = weight again.

                          --- 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 3WE View Post
                            Ok Evan, you win. If they had made a conservative descent and forgotten the gear, they would not have crashed.
                            If they had made a proper descent (i.e. conservative of human life), it would have been impossible to forget the gear, so there would not have been a crash.

                            What made forgetting the gear possible are the conditions arising from the rushed, overspeeding descent that they did make.

                            Plus everything Gabriel just said about going around after touching down without gear.

                            You can't win this one. TIme to give up.

                            Comment


                            • Please keep dismissing folks that had fake licenses (and the lack of gear) and violated all sorts of stuff and get your descent procedures written so the airline can resume flying.

                              Crews get rushed all the time...go arounds even happen...

                              I don’t give a rats ass how they get down to 1000 feet...AT THAT POINT, get things on target and maybe run a landing checklist...

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

                              Comment


                              • Originally posted by 3WE View Post
                                I don’t give a rats ass how they get down to 1000 feet...AT THAT POINT, get things on target and maybe run a landing checklist...
                                Well, it seems we are finally starting to converge here (you and me, maybe not Evan).

                                But this is not what happened. Then never got things on target, gear or no gear.

                                --- 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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