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Qatar Airways B77W hit airport approach lights on departure, flight continued

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  • #61
    Evan,

    The distance between 0 speed and rotation start is 2300m.
    The speed at which rotation started is 191kts.
    That gives you an average acceleration of 4.08 kts per second, which is a quite typical lower bound for a big twin jet at MTOW (be it the structural MTOW or the climb-gradient restricted MTOW, for example in high'n hot situations no matter how long the runway your MTOW is limited by the second segment climb gradient with an engine inop. The climb gradient is very strongly correlated to the thrust/weight ratio, and the acceleration IS the thrust/weight ratio). Even with a reduced take-off thrust (again, if your lowest thrust is limited by the second segment climb gradient with an engine out, so with a heavy airplane there is only so much you can go down with the take-off thrust regardless of the runway length)

    I must warn, however, that the distance is extremely sensible to small changes in the acceleration. 3.58 kt/s (just 1/2 kt/s less) would give you 300 meters more of distance.

    The airplane ate another 586m (to a total of 2866m) in the 5 seconds between the rotation start and the actual lift off.

    And then it sould was likely a few hundreds of meters more since lift-off to 35ft.

    And then add more distance for the reduced acceleration between V1 and 35ft had an engine failed at V1.

    With that performance, the computed take-off distance (from zero speed to V1 with both engines, engine failure, from V1 to 35ft and V2 with one engine) for the real thrust setting used would clearly be several hundred meters past 3000m. Runay 09 is some 3600m long. So we have an approximate match.

    Additionally:
    The pilot elected to compute an optimized take off thrust, got an assumed temp of 36 C, and printed out that output for reference.

    With all that in mind, I don't see any reason to believe that the pilot used full thrust instead of the calculated reduced thrust. It could be, but it's not like anything in the performance can make you think so.

    The report will tell.

    --- 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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    • #62
      Oh, and by the way, maybe it's splitting hairs, but these reduced thrust take-offs are not "derated thrust". In a derated thrust take-off you cannot use more thrust than the derated one. Derated thrust take-offs are rare (especially in twins), and used only when the limiting factor affecting the take-off performance is Vmcg. A reduced thrust lets you reduce Vmcg. But if an engine fails at V1 and you add thrust, you might loose control.

      In the "normal" reduced thrust take-offs, like this one, that some manufacturers call "take off flex" or flexible take off, the pilot can increase to rated thrust at any time.

      --- 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


      • #63
        Originally posted by Gabriel View Post
        With that performance, the computed take-off distance (from zero speed to V1 with both engines, engine failure, from V1 to 35ft and V2 with one engine) for the real thrust setting used would clearly be several hundred meters past 3000m. Runay 09 is some 3600m long. So we have an approximate match.

        Additionally:
        The pilot elected to compute an optimized take off thrust, got an assumed temp of 36 C, and printed out that output for reference.

        With all that in mind, I don't see any reason to believe that the pilot used full thrust instead of the calculated reduced thrust. It could be, but it's not like anything in the performance can make you think so.

        The report will tell.
        Hmmm, ok. Well, what I get from the 773ER FCOM I am holding is that it is weight-limited above 347,000kg at 3000' from brake release to clearing a 5m obstacle beyond the runway, meaning at that TOW it requires about 3000m to safely clear that obstacle with what I assume is full thrust and assumes 1 engine out after V1 (and a healthy margin of clearance). This one was 342,000kg with two good engines and used about 3000m from brake release to striking the approach lighting. But there are a lot of unknowns in that and I'm not saying it can really determine whether full thrust was used.

        Oh, and by the way, maybe it's splitting hairs, but these reduced thrust take-offs are not "derated thrust".
        Ok, right, I see a lot of references (including in the FCOM) to "assumed temperature derates" and thus just refer to them all as such but I realize that is not technically-correct terminology. I can see in the report that 'assumed temperature thrust of 36°C' was used (OAT+7°), not like TO1 or 2 derate. But, since the thrust seems to have never been manually increased, another reason to suspect it was already at or nearly at full power.

        Comment


        • #64
          BTW - Not the first time a 777 crew has gotten into this mess:

          Two passengers attempted to stop a British Airways Boeing 777-200 from taking off from a Caribbean airport last September, after realising


          Investigation into the accidental short-field departure by a British Airways Boeing 777-200 at St Kitts has revealed that the taxiway misidentification which...

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          • #65
            I remember that case. And wow: "Despite the shorter runway distance, the 777 became airborne in about 860m". Certainly it was not anywhere close to MTOW, but still wow.

            --- 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 Evan View Post
              I don't get this. Doesn't 09#T1 mean departure from the T1 intersection? If so....
              That is what the first officer thought too, but it doesn't. It actually means Runway 09 with Temporarily displaced threshold!

              Originally posted by AVHerald
              ...the Electronic Flight Bag. That tool offered only one option 09#T1, which is being understood as a runway full length takeoff.

              ...

              The commander requested the operating first officer to advise ATC that they were able to depart from intersection T1. The first officer glanced at his notes and saw he had written ‘09/(T1)#’, which made him believe that this was an acceptable line-up point for take-off, he called ATC advising them that they were able to take T1 for departure from Runway 09.
              But a commentator was kind enough to explain the cryptic codes used by the OPT:


              Originally posted by AVHerald
              Meaning of T1
              By Baade152 on Tuesday, Dec 8th 2015 03:12Z

              @ mighty Q

              T1 as Temporary 1. Used on OPT for temporary runway reduced length.
              Unfortunately for the crew, this airport also has a taxiway named "T1" and on top of that the T-numbers count up towards the threshold, not away from it.

              Comment


              • #67
                Originally posted by Gabriel View Post
                I remember that case. And wow: "Despite the shorter runway distance, the 777 became airborne in about 860m". Certainly it was not anywhere close to MTOW, but still wow.
                That was a -200. I wonder how much the 'brakestand' shortens the takeoff length.

                Comment


                • #68
                  Originally posted by Spectator View Post
                  That is what the first officer thought too, but it doesn't. It actually means Runway 09 with Temporarily displaced threshold!



                  But a commentator was kind enough to explain the cryptic codes used by the OPT:




                  Unfortunately for the crew, this airport also has a taxiway named "T1" and on top of that the T-numbers count up towards the threshold, not away from it.
                  Which begs the question: why didn't this crew understand the terminology of their own computer interface?

                  Comment


                  • #69
                    Originally posted by Evan View Post
                    Which begs the question: why didn't this crew understand the terminology of their own computer interface?
                    Maybe because it was cryptic?
                    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                    Comment


                    • #70
                      Originally posted by Evan View Post
                      That was a -200. I wonder how much the 'brakestand' shortens the takeoff length.
                      Ok, but I doubt that changing 300LR to 200 is enough to explain all of the reduction from 3000+ to 860.

                      The brakestand will of course reduce the take-off run, but not by much, because the plane would have moved forward very little (a couple dozens of meters) until reaching 55% (that is when they released the brakes). But even that can make a difference in extreme cases.

                      --- 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


                      • #71
                        Originally posted by Evan View Post
                        Which begs the question: why didn't this crew understand the terminology of their own computer interface?
                        They did. All of them (including the relief crew) understood that it was going to be a full length take-off. Initially.

                        --- 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


                        • #72
                          Originally posted by Gabriel View Post
                          Ok, but I doubt that changing 300LR to 200 is enough to explain all of the reduction from 3000+ to 860.
                          Well there is tremendous difference in takeoff distance between a light -200 and a -300ER near MTOW. A light -200 can legally takeoff from a 5000' runway. A heavy -300ER would need twice that. Still, 860m is damned impressive!

                          They did. All of them (including the relief crew) understood that it was going to be a full length take-off. Initially.
                          But then what the hell does this mean?

                          As they taxied along S the commander decided that the aircraft could depart from the runway intersection T1. He could not recall why he made that decision, but believed it may have been because the printed information displayed ‘Runway 09#T1’ in a compelling way.
                          "Compelling"? It displayed it as:
                          RUNWAY : 09#T1
                          If they understood the meaning of that, why would that be 'compelling'?

                          And why did the F/O jot it down as: 09(T1)#?
                          The first officer glanced at his notes and saw he had written ‘09/(T1)#’, which made him believe that this was an acceptable line-up point for take-off, he called ATC advising them that they were able to take T1 for departure from Runway 09 .
                          It really seems to me that the meaning was unclear to him.

                          Comment


                          • #73
                            Originally posted by Evan View Post
                            Well there is tremendous difference in takeoff distance between a light -200 and a -300ER near MTOW. A light -200 can legally takeoff from a 5000' runway. A heavy -300ER would need twice that.
                            That's my point. You are comparing a LIGHT 200 with a HEAVY 300ER. I bet my lunch that LIGHT/HEAVY has more to do with it than 200/300ER.

                            But then what the hell does this mean?
                            It means that, initially, all of them understood that it would be a full length take-off.
                            The operating crew calculated the take-off performance figures for Runway 09, using the On-board Performance
                            Tool (OPT) contained within the Electronic Flight Bag (EFB) using a take-off weight of 342,000 kg. The OPT
                            offered the crew only one option for Runway 09, which was ‘09#T1’ as displayed by the OPT. This was understood
                            by the crews to mean Runway 09 full length
                            Then, for a number of factors (of which poor understanding of the OPT can be one of them) the captain changed his mind and the rest of the crew actively or passively backed him up.
                            Other factors include the name of the T1 taxiway (that happens to be the same than the code of the OTB for a full available length take off), the misleading cropped image of the airport diagram in the EFB, the plane landing just inf front of them at T1, and poor CRM.[/quote]
                            It really seems to me that the meaning was unclear to him.
                            Evidently it was not clear enough. That's why I said that they INITIALLY understood that it meant a full length take-off. The relief crew even questioned the Captain when he changed his mind,m then poor CRM kicked in.

                            --- 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


                            • #74
                              Originally posted by Gabriel View Post
                              It means that, initially, all of them understood that it would be a full length take-off.
                              I don't buy that. I think this kangaroo report is hiding some realities that need to be addressed. Hopefully the final report will address them.

                              I think what the crew understood when they saw 09#T1 was "Runway 09 (full runway) and, uh, some technical shit, who cares" and then, when intersection T1 appeared on the EFB map, the PIC thought, "ahh, yeah, that's what #T1 meant!". Same with the F/O when he saw the intersection and looked at his notepad.

                              I still going with non-standard terminology on this one. And would it kill them to make it 09#TEMP1? There is an obvious danger exposed by this incident in adding abbreviations that match runway intersections.

                              Comment


                              • #75
                                Qatar Airways CEO Al Baker's statements: https://www.flightglobal.com/news/ar...iami-c-419912/

                                "At no time was the aircraft or the passengers put in any harms way."
                                “Such kind of incidents happen quite often, either it is a tail strike on the runway or it is contact with the landing lights,”
                                WHAT??!

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