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This video shows a 737 'near miss' takeoff. I'm curious as to why the aircraft did not take off as expected, i.e. is there anything obvious from the video?

I'm assuming the speed and payload would have been within the expected limits, so wondering if someone can explain what happened.

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    $\begingroup$ @RonBeyer While the actual reason cannot be guessed indeed, a short list of most likely causes is all the OP is looking for. No need for armchair piloting, no need for making a phd thesis out of it. $\endgroup$ – bogl Oct 23 '18 at 15:52
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    $\begingroup$ Note that in spite of what the title says the aircraft didn't seem to actually stall, it just was too slow to climb out of ground effect. It can't stall at this point, because it is “geometrically limited”, which means the pitch angle for tail strike is lower than the angle of attack for stall and it is moving horizontally, so you can meaningfully compare those two angles in this specific situation. $\endgroup$ – Jan Hudec Oct 23 '18 at 17:26
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    $\begingroup$ I did notice the air crew didn't have flaps set. They appear to be at 0°. If they calculated their Vr speed for 15° flaps, then they would have rotated too early. $\endgroup$ – BillDOe Oct 23 '18 at 19:29
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    $\begingroup$ I don't really agree with the close votes here. There are basically only two realistic possibilities: they calculated Vr incorrectly for their configuration and situation or they began rotating before they reached the calculated Vr. $\endgroup$ – reirab Oct 23 '18 at 20:37
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    $\begingroup$ I disagree that this question should be put on hold. There are good, insightful, and important comments and answers to the OP's question. If we split hairs on questions that arguably may be asking for an opinion vs factual response we would have to throw out many more questions. So many of the "answers" to questions posed are opinion based. A lot of good information will be lost if this question is not available to those seeking similar insight. Too much "form" over "function" will under-serve this site and experienced, knowledgeable people will leave as a result. Just my two cents. $\endgroup$ – 757toga Oct 24 '18 at 0:43
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It looks to me like a too-early rotation (lifting the nose off of the runway). This may have happened as a result of a miscalculation of the rotation speed (known as Vr speed). A miscalculation of the Vr speed, for example, can happen if you derive this speed using a lower than actual aircraft takeoff weight in your performance calculation. This would lead to a calculated Vr speed that was less than was required.

If this was the case, as the pilot rotated the aircraft into the liftoff attitude there would not enough speed to allow the aircraft to climb out. Instead the aircraft would stay on the ground (or in ground effect) until it accelerated to the proper lift off speed.

The crew could also have miscalculated the power setting necessary for takeoff by using an incorrect temperature, or physically failing to advance the thrust levers to the correct position. Since the B737 in the video was a later model it likely had a Flight Management System (FMS) that would have calculated the takeoff thrust setting based on keyboard entries made by the crew.

Also, it's common for the takeoff thrust to be set, based on the FMS calculated values, using the auto-throttle function (sometimes takeoff thrust is manually set by the crew using the calculation provided by the FMS[or similar]). In other words, after initially moving the thrust levers forward a bit, the pilot would just push a button on the mode control panel and the throttles would automatically move to the proper takeoff setting. Again, this would depend on the proper information being loaded into the FMS/FMC so that proper calculations for Vr speed, thrust setting, etc. would be utilized.

There are many variables depending on what procedures the crew used and the pilot technique, but the video shows the airplane rotating and not lifting off, and just my opinion, but this was likely because the rotation was started at a lower speed than was appropriate.

Here is a link to a incident involving a B737 that appears to have some similar circumstances.

B737 tail strike

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    $\begingroup$ The leading edge flaps were extended with no trailing edge flaps (i.e. the "flaps 1" setting,) which is a valid 737NG takeoff configuration, especially on such a long runway. $\endgroup$ – reirab Oct 23 '18 at 20:44
  • $\begingroup$ @reirab - when the trailing edge flaps go to any position (1 or more) the leading edge slats/flaps extend (to some degree based on trailing edge flap position). $\endgroup$ – 757toga Oct 24 '18 at 2:31
  • $\begingroup$ Another possible reason would be wrong cargo weight input. See aviation.stackexchange.com/a/33046/17780 $\endgroup$ – bogl Oct 29 '18 at 12:47
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With the help of the clearly visible livery (Royal Air Maroc), registration (CN-RNV) and approximate time (before August 2016, probably not by too much), I managed to find the specific Incident: Royal Maroc B737 at Frankfurt on Jul 23rd 2016, three takeoffs for the price of one on The Aviation Herald. It even links to the very same video that you do.

Unfortunately:

On Aug 30th 2016 the BFU responded to an inquiry by The Aviation Herald of Aug 25th 2016 stating, the BFU had neither received any notification by the crew, airline or airport involved nor by the person taking the video (see below) and became aware of the occurrence only through the release of the video into the public more than a months after the occurrence. The BFU argued that as result it will not be possible to establish sufficient facts and evidence needed for a detailed investigation, hence the BFU decided to refrain from initiating an investigation.

So we won't have anything better than guesses anyway.

The article does speculate that the wake turbulence of the landing aircraft crossing above the runway just before might have affected it, but it was too close to the starting point and is unlikely to have this effect, so what remains is that the pilot flying started to rotate too early. There may be basically two reasons for that:

  • The pilot flying started rotating before appropriate speed was reached, or
  • they calculated lower rotation speed (Vr) than they actually needed.

The take-off procedure with the speed call-outs made by the pilot not flying is the same for every take-off, so the second reason seems more likely.

The rotation speed depends on weight, density altitude and flap setting. Inserting wrong weight is probably most common reason for this type of incident, but calculating for higher flap setting than they used is a believable option here too as they used rather low setting for the actual take-off.

It should be noted that the pilot realised their mistake and handled it correctly by lowering the nose back to let the aircraft gain enough speed first.

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It looks like a case of the flight crew using an incorrect flap setting for the takeoff and calculated Vr. Looking at the video, there was very little flap deployed though the LE flaps and slats were extended. The airplane struggles to become airborne then settles back down on the runway after attempting to exit ground effect. The crew apparently realized the airplane wouldn’t fly, so the allowed to to remain on the runway, gain additional airspeed, then rotate and fly off when there was no alternative left. Major safety violation there and could have caused an accident. Fortunately there was ample runway to do so on.

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  • $\begingroup$ I seem to recall several 737 pilots stating after this incident that this is the "flaps 1" configuration for a 737 and that it's a perfectly valid takeoff configuration. Though you're right that it might not be the configuration for which they calculated Vr. $\endgroup$ – reirab Oct 23 '18 at 20:33

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