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I recently watched MenTour Pilot's new video about the Royal Air Maroc 737 takeoff from Frankfurt several years ago that made the news at the time because it rotated, failed to fly away at high AoA for several seconds, lowered pitch and settled back to the runway, accelerated some more, and then took off normally.

The original video of the incident is here:

In his video, MenTour Pilot suggests that the 737 was prevented from taking off because of the sudden drop in airspeed from encountering the left wingtip vortex of the A330 that had recently landed on a nearly perpendicular runway. However, the original video seems to show the RAM 737 at high AoA for around 11 seconds after its first rotation attempt. At Vr for a 737, that seems like it should burn through 2,000 to 3,000 feet of runway, depending on weight. (135 kt = 228 ft/s, for example)

So, my question is, how wide is each wingtip vortex of a landing A330 around 1 minute after landing? The conditions appear to be almost calm wind. Would each vortex really be thousands of feet wide by that point?

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    $\begingroup$ Without knowing the details of this specific incident, it has happened before that a too low take-off mass has been used for performance calculations. The resulting Vr will be lower and the situation may be aggravated by choosing a lower power setting (derate / assumed temperature) to save on engi e maintenance. In that case most of the runway will be used by the time the crew discovers the aircraft does not fly at Vr $\endgroup$
    – DeltaLima ♦
    Commented Feb 26, 2021 at 21:39
  • $\begingroup$ @DeltaLima Yep. And, personally, I think that's probably what happened (computed either for wrong mass, a different t/o config, or both,) but I was curious how big the wingtip vortices would actually be at that point anyway. Thousands of feet seemed really excessive. I know when I've hit my own wake in light aircraft, even after making a full 360 turn, the spread was almost nil and hitting the wake was more just like a single jolt, not an effect spread over time. But, of course, an A330 is much larger and faster than a PA-28. - haha $\endgroup$
    – reirab
    Commented Feb 26, 2021 at 21:45
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    $\begingroup$ For those interested: avherald entry. Spoiler: no investigation, and the airline's statement says deliberate pilot action to increase speed after being notified of the wake turbulence (I'm aware the question isn't about that :)). $\endgroup$
    – user14897
    Commented Feb 26, 2021 at 21:51
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    $\begingroup$ During last summer I've spent a few days time at & near the taxiway next to position where this aircraft got airborne for the first time. I don't remember seeing any aircraft rotating that early, and due to lack of passengers, take-off weights were low this summer. Another hint is that rotation is approximately 20 seconds after application of take-off thrust. In my experience, the rotation is usually after ~33 seconds on the 737-800, perhaps a few seconds earlier on the -700. This was a very early rotation by all means. $\endgroup$
    – DeltaLima ♦
    Commented Feb 26, 2021 at 22:06

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Vortices of large aircraft often move laterally at speeds of 2-3 knots when they sink to within 100-200 feet of the ground.

In calm wind conditions, vortices created by large aircraft during landing operations can remain for many minutes over the normal touchdown area. They can also slowly drift from one runway to a nearby parallel or crossing runway. (NASA; emphasis mine)

and

enter image description here
Source: FAA

Using the two pieces of information above, the vortices start moving laterally at say T+15'. At T+60' (45 seconds later) they would have covered a lateral distance of 150–225 feet. In windier conditions they would travel farther downwind but dissipate quicker.

The day the video was taken (July 23rd, 2016) there were winds in daytime but almost all the reports having the direction variable, e.g.:

EDDF 231150Z 03005KT 330V110 9999 BKN023 SCT080 24/18 Q1017 NOSIG=

Assuming for the sake of simplification that the variable wind lessens the travel/dissipation, and plotting 650 feet (225 each direction + ~200 feet wingspan) on Google Earth on the affected runway, this result is shown below.

The core is surrounded by an outer region of the vortex, as large as 30 metres in diameter, with air moving at speeds that decrease as the distance from the core increases. (CAA New Zealand via skybrary.aero; PDF)

For the core diameter above, that would be a radius of ~50 feet at each end for a large plane.

enter image description here
About 3,200 feet down runway 18

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    $\begingroup$ The rotation of the Royal Air Maroc 737 started approximately 650 meters into the take-off roll, about 160 meters north of the red line. $\endgroup$
    – DeltaLima ♦
    Commented Feb 26, 2021 at 22:46
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    $\begingroup$ @reirab: see update $\endgroup$
    – user14897
    Commented Feb 26, 2021 at 23:06
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    $\begingroup$ @ymb1 Thanks! That seems to confirm my suspicion that, if the RAM 737 did indeed roll through the A330's wake vortices (which is completely plausible since they tend to descend over time,) it should have blown through them in around a second (120 kt ~= 200 ft/s,) which means that the explanation given in the video of them rolling through only the left-side vortex for at least 11 seconds doesn't add up. $\endgroup$
    – reirab
    Commented Feb 26, 2021 at 23:13
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    $\begingroup$ @ymb1 That windsock appears to be fairly close to the runway. They pass it right in the middle of the failed rotation. If it’s a wake turbulence encounter why did the windsock not move. My immediate reaction when I saw the video was that the plane was heavier than the pilots expected. $\endgroup$
    – TomMcW
    Commented Feb 27, 2021 at 3:48
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    $\begingroup$ They flow bottom to top (high pressure to low pressure), so outward from the centerline. youtu.be/dfY5ZQDzC5s?t=331 $\endgroup$
    – DeltaLima ♦
    Commented Feb 27, 2021 at 21:06

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