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Final Report: April 2018 737 high speed aborted TO

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Final Report: April 2018 737 high speed aborted TO

Old 30th Jan 2021, 10:46
  #81 (permalink)  
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Well, if the aircraft doesn’t fly after V1, it’s unflyable.
I’m a firm believer in the V1 consept, but I also believe in Murphy.
«That can’t happen» doesn’t apply to me,
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Old 30th Jan 2021, 14:28
  #82 (permalink)  
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Surprised that no-one has mentioned flex take offs as a contributory factor.

There have been some serious brown trouser moments when flex calculations have been incorrect, even a correctly calculated flex take off gives less runway if something goes wrong. I can't find statistics on flex related accidents but I'm certain that the bean counters win with increased time on wing and maintenance costs for engines.
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Old 30th Jan 2021, 14:29
  #83 (permalink)  
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No-go after V1?

I don't have the statistics to hand.

I would hope the relevant authorities do have the statistics to hand.

The official advice given about when to attempt a no-go after V1 should be followed. Such advice is normally generated by people's deaths. Discussing individual cases is pretty fruitless as what is important are the overall statistics and the criteria by which the statistics are judged. If you want to criticise that method from a position of knowledge, go ahead: but using individual cases to argue a point isn't really helpful due to all the biases involved, most of which are unwitting.

The other things to remember are that:

(a) Hindsight is a wonderful thing, beloved of 'armchair quarterbacks' the world over. Analysing a situation from the relaxed position of having enough time to think things through and being in possession of the relevant facts is vastly different to making a decision in the heat of the moment.
(b) Simulators are artificial. You know you do not have a bus-load of souls behind you. You end up treating things in a different way, some better, some worse.

There is room for individual decision making. As a captain you have that right, which also has a heavy responsibility. There are times when declining to follow the official guidance is the right thing to do, and if you get it right, you might be a hero, and if you get it wrong, you will be responsible for bad things happening. Rules are for the guidance of wise men, and wise men know their limitations.
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Old 30th Jan 2021, 14:49
  #84 (permalink)  
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My final word on this subject. It may come as a big surprise that simulator instructors / examiners are also real world pilots (including me) and very aware of both their responsibilities and real world scenarios. Simulators are regulated to a very high fidelity and are not toys. You may not lose your life in one but you can certainly lose your licence. Rules in commercial aviation are defined by regulatory authority and are not merely for guidance but adherence that is if you wish to remain employed. Nobody is a hero and in professional aviation we just try to do our jobs properly and recognise if they are not. It’s called professionalism based on years of experience and study. The only reason I have engaged is to dispel the dangerous misinformation and lack of even basic understanding of jet transport performance displayed in many of the posts here.

Last edited by olster; 30th Jan 2021 at 15:05.
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Old 30th Jan 2021, 14:56
  #85 (permalink)  
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No it is not. It is generated by statistics showing that usually when rejecting above V1, the PIC gets it wrong and does so for an insufficient reason. However, those same statistics show that in a smaller proportion of these cases, the abort was actually justified! That should be the end of the debate right there! Another member posted one such study several posts up. Look it up.

As for individual cases, I just enumerated them so you can see the severity of the accidents vs loss of control on takeoff accidents. These are the actual numbers - 317 human lives lost in 40 years from high speed aborts - and we're talking everything from V1 to x knots above Vr. We're talking cases where the aircraft got airborne twice and still they rejected and the net result was better almost every time than continuing with a non-flying aircraft. If you don't believe me, do your research.

As for the members accusing everyone who doesn't agree with them of being flight sim drivers, that's just disgusting. If you wanted to see some credentials, you could have asked in a civilized manner over PM.

This is the last time I participate in such debates. Take your chances on the ground or take your chances in the air, in the end you alone will be judged for your actions.
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Old 30th Jan 2021, 16:15
  #86 (permalink)  
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Take your chances on the ground or take your chances in the air, in the end you alone will be judged for your actions.
I’ll take my chances on the ground thank you.
What is indeed disgusting is the pedantic attitude and the cherry-picking.
Its been said already and I’ll repeat it, he buggered up the RTO.
To focus solely on the reason for the RTO is not seeing the entire picture.

“Airplane unable or unsafe to fly”
Now they had no annunciation but have a read and consider rejecting after V1 and going off the end or taking it “flying”

Similar event:


Now sit back in your armchair and reconsider the above two examples in some of the highest mountainous terrain in the world...at night...with weather.
I’d be more then happy going off the end in these cases.
I’ll even shred my license as I’m walking away from it.
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Old 30th Jan 2021, 17:04
  #87 (permalink)  
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To focus solely on the reason for the RTO is not seeing the entire picture.
There has been a lot of back and forth on this thread and from my POV, posts that seem more directed at "winning" the argument than contributing to expanding understanding of what and more importantly WHY this event happened.

I like reading PPRuNe because there are often ideas expressed that force me to challenge my assumptions on important issues. And numerous times I have been forced to reconsider things I thought were obvious and not worthy of debate.

B2N2's, quote above, to me, really summarizes the issue.

When I first read the report I have to admit my first thought " Oh Yah some third world crap airline went off the runway after they totally pooched the RTO and this would never happen to me", then I thought of a takeoff I did at Terrace British Columbia (CYXT) one really, really nasty night. We had a long discussion about getting out of the valley if various bad things happened but they were all considerations for after we got airborne. The part from max power to V2 was just the standard brief. I remember letting go of the brakes after the stable power call and thinking only about getting safely out of the valley. I like to think if a similar issue ( i was not flying a 737) had occurred I would have acted perfectly but thinking back I am now not so sure. You can be mentally behind the airplane but you can also be mentally too far ahead of the airplane.

From a human factors POV I think this was a significant factor in this incident. Combine the mental model the captain had at the beginning of the takeoff roll flying out of a very challenging airport, with evidence of incomplete/poor training and you have this result. Even in reputable Western airlines there has been constant pressure to reduce training costs which has IMO led to a very tick the box culture developing in sim training sessions. So if all the boxes are ticked the pilot must be fully trained, right ? This would never happen to a us flying for a real airline, right ?

Finally I think it is worthwhile to acknowledge that after the aircraft came to a stop there was some good CRM happening. This could easily have turned into a full evacuation with probable injuries if he FO had not made some good recommendation to the Captain which the Captain accepted.

The take away for me, and I think it is important to note this is a personal take away not advocacy for a particular action as the "right way" to do things; Is a reinforcement that regardless of the situation, when the power levers go up the importance of having my brain engaged totally on what is happening from now to Vr, not on what might happen later in the departure.

Last edited by Big Pistons Forever; 30th Jan 2021 at 18:47.
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Old 30th Jan 2021, 19:20
  #88 (permalink)  
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Stuka, you're missing the point. On the above list, on how many did the crew learn of something after V1 but before they attempted to rotate? Most of those the aircraft were not flight worth at the beginning of the takeoff run (generally mis-configured with an inop or disabled warning system). If the aircraft won't rotate, you're generally not going to discover that until you attempt to rotate - at which time you better pray there isn't much to hit at the end of the runway.
The only one that really fits the scenario of the crew getting some sort of indication of trouble after V1 is Concorde - and they were going so fast when the tire blew that even if they'd tried to abort I doubt it would have ended much better.
The question is, should you abort if you get an indication of a problem after V1. The Boeing answer was no...
Pointing out that aircraft that are not airworthy at the beginning of the takeoff run often crash is a non sequitur.
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Old 30th Jan 2021, 21:35
  #89 (permalink)  
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Stuka Child.

I hope you continue to participate - your knowledge, experience and opinions are valuable and worth sharing.

Beamr posted a link to an interesting (and I hope, informative) study: NLR Air Transport Safety Institute: REJECTING A TAKEOFF AFTER V1...WHY DOES IT (STILL)HAPPEN?

The inclusion criteria for data analysis were:

The following criteria were used to establish the data sample:
•Only occurrences that were classified as ‘accidents’ or ‘serious incidents’ according to ICAO Annex 13 definition were included;
Both fatal and non-fatal accidents were included;
•The accidents and serious incidents involved a high speed rejected takeoff in which the abort was started after V1 (the actual decision to abort could be before V1);
•Accidents related to unlawful or military action were excluded;
•The occurrences involved fixed wing aircraft with a maximum takeoff mass of 5,500kg or higher that were used in a commercial operation (passenger or cargo) including training and ferry flights. There was no restriction to the geographical location of the occurrence;
•Both turbofan and turboprop aircraft were considered. Piston engined aircraft were excluded; •The accidents occurred during 1980 through 2008.
As far as I am concerned, the inclusion of fatal accident data means that the data are generated from peoples' deaths. Hard won statistics.

Note that I am not saying one should never abort after V1. Obviously, things are far more nuanced than that, and as the report linked to by Beamr says:

•Pilots have difficulties in recognising “unsafe to fly” conditions;
•The Detection-Decision-Action process still takes a lot of time!
Despite these difficulties, in the period 1994-2008, for the incidents analysed, 31.9% of the decisions to abort were correct (44.4% were not, with the remainder unknown)

I have neither the experience or knowledge to evaluate what happened in Kathmandu, and the multiple opinions in this thread show that it is not cut-and-dried. What we know from statistics is that many RTOs are unjustified. Some, however, are not, and we are arguing/debating/discussing how to tell the difference. It isn't always easy.

I'll thank you again for your engagement. I think we are on the same side, but maybe on different wings (football, not aircraft).
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Old 30th Jan 2021, 23:08
  #90 (permalink)  
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I am sorry if I came across as confrontational. I apologize for that, it was never my intention to write as if we were arguing. My "steam" was mostly directed to a particular set of posters who insisted dogmatically that to even contemplate aborting above V1 meant you don't know what you're talking about, you are not in the industry, etc.. You are absolutely right that people have indeed died in these tragic accidents, and sometimes looking at numbers and statistics one forgets that these were actual beings with their own inner universes, with their own emotions, and that is something that cannot ever be measured. Even one fatality is too much.

I guess what I'm trying to do here is to churn up some ideas that we can all maybe think about in order to at least increase the chance of survival if - God forbid - we are confronted with such a situation one day. As you said, 31.97% of high speed RTOs in that study were judged correct. That is a mighty high percentage, which in itself completely disproves the notion that V1 means continue at any cost. Now, as you say, how to tell the difference between something catastrophic is happening vs. I can fly this? Or between this plane is never getting off the ground (or will only come down harder if it does) and let's just grab some more airspeed and hope? In the heat of the moment, it is a nasty choice to make, knowing that you might kill people either way. Only thing we can do is be prepared - knowing the airport, knowing the aircraft and having some personal criteria set down. Beyond that, it's just instinct. Could turn out right, could turn out wrong.

For the incident at hand, I can understand why the Captain made this decision and even the relevant authorities are in agreement. Just to get a visual idea, this is the outcome:

No injuries, aircraft is fine, and keep in mind this was not a properly executed RTO.

Thank you for keeping the discussion going, I think there is great potential for all of us to increase our understanding.


The point remains the same, whether something catastrophic happens after V1, or whether you realize as you try to rotate that your aircraft won't get off the ground, or that if it does it will only be controllable for a short time. The fatality rates are clear: if an accident is bound to happen one way or the other, you drastically increase everyone's chances of survival by staying on the ground and slowing down as much as possible before you hit whatever is in front of you VS. forcing her up into the air and hoping she'll go and starting to hit stuff with the engines running at takeoff thrust or pancaking it in from the sky. I'm not saying it's an easy call to make. But it is something to think about.

If you have time, look through the accident reports as I have and also through some of the non-fatal incidents. Many of these high speed RTOs were obviously wrong calls. If they had continued, everyone would have lived. But there were quite a few right calls as well. And I'm talking rejecting well after rotation, forget about V1.

Think of it this way. You are in what you believe to be an unflyable/uncontrollable aircraft as you are rotating or trying to. If you take your chances on the ground and get it wrong, you will kill 16 people on average in case of a fatal accident. A common number is between 1 and 3 fatalities. If you take your chances in the air and get it wrong, you will on average kill almost everyone on board in case of a fatal accident. These are the stakes.

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Old 31st Jan 2021, 08:38
  #91 (permalink)  
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I have no issue at all with the crew's decision to reject the take-off. They received an unambiguous indication that the aircraft wouldn't fly safely but were hamstrung by the fact that they were in, essentially, a 50-year-old aircraft with no further information about why that might be. If you gave me a config warning at V1 I'd be thinking about an uncommanded flap retraction, or speedbrake deployment, or trim runaway - all of which would lead to loss of control very quickly.

The aircraft would have stopped on the paved surface if they hadn't disconnected the autobrake, which is really the only learning point I'd take away from this.
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Old 31st Jan 2021, 09:29
  #92 (permalink)  
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One of the unwelcome elements of PPRuNe is it's ability to polarise topics, which then creates factions, something this thread demonstrates very well.

Having taken a side, IMO it does reduce any objectivity. If you believe you can argue either side of the argument and still sift the wheat from the chaff, carry on.

What I do find ironic is that some of the go minded posters are also the one's who would criticise "Children of the magenta line"
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Old 31st Jan 2021, 11:45
  #93 (permalink)  
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Stuka, focus on emotive fatalities can lead to unbalanced conclusions.
Historical risk, with known outcome and statistical probability is a measure of what happened, but more often not suitable for judging future risk requiring statistical inference. The future does not follow the past.
Past probability is not always suitable (e.g. 737 Max should not happen again).
Also, the outcome in future events is unknown, particularly fatalities - circumstance, aircraft size, passenger load, etc.
As in previous posts, there are very few if any actual 'catastrophic' (n.b. emotion) events after V1, but far more issues prior to takeoff.

A good comparison with this event is the CRJ overrun at Charleston - mis set flap, then config alert after the crew reselect during the takeoff. RTO after V1, saved by EMAS.
The outcome risk in each of the accidents appears similar, overrun mitigated by EMAS or 'mud'; but considering future risk - without mitigation, the difference between the steep drop off the end of 23 CRW, or more grass at KTM, would influence our judgement of 'risk' (likelihood of harm), … for an event which more likely is initiated before takeoff.

momoe; the problem with the much quoted "Children of the magenta line" is that it fails to explain how we achieve the awareness and then decide to 'click click'; aspects central to this incident.

Background reading 'Decisions under Uncertainty'
Follow the links to parts two and three:-
2 Two types of Ignorance; … we live in a world where we are, to some extent, ignorant, then the best course is “thoughtful action or prudent information gathering.” Yet, when you look at the stories, “we frequently act in ways that violate such advice.”
3 Avoiding Ignorance; … our “illusion of predictability.”

Also; a view of reality, situations and decision making are not clearcut, not black or white arguments.
Conditions for Intuitive Expertise 'A Failure to Disagree'
Under what conditions are the intuitions of professionals worthy of trust?
True experts, it is said, know when they don’t know. However, nonexperts (whether or not they think they are) certainly do not know when they don’t know.

Last edited by safetypee; 31st Jan 2021 at 14:44. Reason: Typo
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Old 31st Jan 2021, 19:07
  #94 (permalink)  
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tdracer has a point, you are not comparing like with like. I have taken the time previously and again today to look at the cases you cite of "crews forcing an unsafe aircraft into the air..." and your argument only holds true if the pilots knew at the time that their aircraft was unsafe. The Northwest accident is a classic in this respect - there was no evidence to suggest the T/O Config warning was available, as the warning horn was not present on the CVR and the CB was found in the popped/pulled position; that crew would likely have been unaware there was a problem until the first indications of a stall, when the natural reaction is to try to fly your way out of it, not close the throttles and accept an over-run. Similarly with Bek Air (failure to de-ice) and the Havana B732. Throw in some startle and surprise, and you can expect people to try to make the circumstances fit the their mental model. Would any of those crews have known - without the benefit of hindsight - that an RTO was safer than V1? Would they have had time to think it through? I doubt it.
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Old 1st Feb 2021, 06:01
  #95 (permalink)  
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The uncertainity factor in stop or go situations is often critical. Particularly if the runway length is marginal and it is night time.

For example, I was jump seating when a Boeing 737-200 took off on a performance limited runway at night. That means a rated thrust bleeds of takeoff which usually means a real kick in the back at full power. At the far end of the runway was a road, then large boulders that formed a sea wall with a drop of 20 feet into the Pacific ocean. A motor bike policeman was stationed on the road to stop traffic until the airraft was airborne.

What we (the captain, the first officer and me as a pilot observer) did not know was that insects and blowing phosphate dust from a nearby phosphate mining area had already blocked the entrance to the Pt2 sensor situated at the front of the P&W JTD-17 engines. So when the first officer applied power to achieve 2.18 EPR at 101% N1 the captain took over the thrust levers and set 2.18 EPR. The engine instruments of N1 and N2 are quite small and the instrument lighting was set low because of the sheer black Pacific night.
In fact, although the EPR gauges showed the needles on 2.18 it turned out to be in this case, a false reading similar to the iced up Pt2 tubes of the Air Florida 737-200 that crashed into the Potomac River at Washington.

Passing one third of the way down the 5200 ft runway of this Pacific atoll, I had an uneasy feeling that the acceleration wasn't the kick in the back that I had been expecting. I leaned forward to get a better focus on the N1 gauges to confirm their readings agreed with the expected 2.18 EPR. I was not wearing my glasses at the time and it was difficult to see the exact reading of the needles of the N1 gauges because of the small graduations. The difference between 101% N1 and 90% N1 was about 4 millimetres.

As I was focusing on the readings of the N1 gauges, I noticed the captain was rapidly glancing ahead at the runway remaing then back at the instrument panel. I wondered if he had the same feeling of unease as me. With the end of the runway coming up fast, it suddenly dawned on me that we were never going to become airborne before the end of the runway - especially as the airspeed was was still approaching V1 with three runway lights to go. At the same time I realised we were in dire straits, the captain acted fast and taking over control from the first officer he firewalled the thrust levers forward against the mechanical stop and hauled back on the control column. . An abort at that point would have been fatal. There was an immediate surge in power as the EPR shot up to 2,30 EPR or thereabouts. . We cleared the threshold and the captain was immediately on instruments. What we didn't know was the jet blast blew parts of the road and sea wall boulders back over the threshold and along the runway. It had been a very close shave. . The policeman blinded by the aircraft landing lights coming closer had already seen the Boeing bearing down on him like an express train and had gunned his motor bike away from danger fast.

At a safe height the captain set standard 1.94 EPR climb power on both engines and commenced flap retraction. During the climb and after the flaps and leading ege devices had fully retracted, we accelerated to 280 knots climb speed. The rate of climb at 10,000 ft was much less than expected. A comparison of climb EPR versus N1 from the manual revealed the N1 was lower than expected;.as was the rate of climb. On a takeoffa few weeks earlier, I had experienced the effect of a single blocked Pt2 sensor which had cleared itself after application of engine anti-ice; even though the OAT was quite high at 25 C.

A simultaneous blockage of both Pt2 sensors at the sea level temperature of 30 C was something I had never heard of before. With both engine readings showing parallel to each other (including EPR and N1) during the takeoff and climb, it was not immediately obvious that we were experiencing a double Pt2 sensor blockage unless one was quick enough to take the N1 readings. Keeping in mind it was night and instrument lighting low.

The captain decided to return to land as the cause of the low rate of climb was not obvious at that point. Fuel contamination was suspected since both engines had identical readings. After touch down, normally 1.6 EPR is used for reverse thrust. I hinted to the captain to use full reverse against the aft stop in case the EPR was mis-reading because at least we knew we were obtaining full reverse. The landing was normal; as was the taxy in. On the ground, the cowls were removed and evidence found of insects and phosphate deposits in both Pt 2 sensors. Both sensors were totally blocked. Hence the subsequent EPR faulty reading. The engineers had forgotten to install covers over the engine intakes during an overnight stop.

Calculations made after the event revealed the actual EPR attained during take off was around 2.07 although both EPR gauges showed 2.18 EPR. A closer check of the N1 during the takeoff would have revealed a figure of around 90% on both engines instead of 101.5%. The fact that all engine readings were parallel to one another led us to believe that all was normal.

On the other hand, if only one Pt2 sensor was blocked it would have stood out as a significant split between the two sets of engine readings and thus the crew would have been alerted at the beginning of the takeoff roll and rejected the takeoff.at low speed. The lesson I took from that event was the difficulty of assessing remaing runway length to go at night and to use N1 as the prime thrust setting and not EPR if fitted.

Last edited by Centaurus; 2nd Feb 2021 at 09:21.
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Old 2nd Feb 2021, 08:41
  #96 (permalink)  
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May have been posted before but Reject after "rotate":

ASN Aircraft accident McDonnell Douglas MD-83 N786TW Detroit-Willow Run Airport, MI (YIP) (aviation-safety.net)
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Old 2nd Feb 2021, 17:48
  #97 (permalink)  
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I don’t think this situation was covered in his set in stone pilot manual, Steinar.
Or he could do what Pinestream said he did in the sim, TOGA and fly by trim. Except that would not have worked either.
What did the report say?

Contributing to the survivability of the accident was the captain’s timely and appropriate decision to reject the takeoff, the check airman’s disciplined adherence to standard operating procedures after the captain called for the rejected takeoff, and the dimensionally compliant runway safety area where the overrun occurred."
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Old 2nd Feb 2021, 17:59
  #98 (permalink)  
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Re the MD83 RTO, #98
The report did not discuss the preflight control check. Would the fault be detectable before flight; it was at some point after flight. A similar servo-tab check on the 146 should have detected the stuck elevator, vice free tab; this check was difficult in a tailwind. The MD83 event discusses wind as causing the damage; similar aircraft have gust dampers, were these working.
Nor does the report consider the certification aspects of dual-path, split control systems, which require the ability to rotate and fly with a single system.

Steinar, 'What would you have done', I expect an honest answer would be that we don't know, because such decisions depend on the situation at the time, as assessed then and there; we were not there.
Questions answered with hindsight (as in the report, with outcome knowledge) might have little relevance to real world outcomes; explanations in the last link. https://www.pprune.org/rumours-news/638276-final-report-april-2018-737-high-speed-aborted-5.html#post10980286
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Old 2nd Feb 2021, 22:21
  #99 (permalink)  
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If find it interesting that those most critical of this discussion, and it is only a discussion, have made no input to it apart from disparaging remarks and “I’m right and you’re wrong”, without presenting facts or any kind of rational argument. Not the way anyone I know who is actually involved in training (or any kind of endeavour) behaves, or should behave.

I don’t think I have seen any suggestion on this thread that rejecting at V1 or above is anything other than a last-ditch method to try and avert/ameliorate a major catastrophe. Most of us will go through an entire career without ever coming close to being put in this position, but there is always the possibility.

We have rules, regulations and standards in aviation to cover a lot of eventualities, with the caveat that when you find yourself in a situation outside the purview of the QRH, etc. you need to draw on all your knowledge and experience and those aforementioned rules become guidelines. It is understandable that those used to enforcing standards find this difficult to grasp, as it is not something which can realistically be trained or assessed. A scenario where the best result is a survivable crash, which is only possible through taking unorthodox action, is not something most would wish as part of an LPC/OPC.

There are a lot of shades of grey here. Taking off from 16L at DOH and birds go down both engines at V1+5, with pops and bangs from both sides with 3,000m+ remaining is a different proposition to a short, wet runway with a very wet or rocky overrun. Is there EMAS installed? Is the V1 we’re using at the high or low end of what is usually a spread? And so on. A good working knowledge of aircraft performance is very useful because it will give you some idea of what might happen if you have to bend/break SOPs through force majeure. Conventional performance is based on losing only one of your powerplants and the configuration of the aircraft being what was planned; as soon as any of those cease to be true, you are on your own and flight may become difficult or impossible.
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Old 2nd Feb 2021, 22:31
  #100 (permalink)  
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Most of those points are covered in the NTSB report:

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