Possible Air Pressure Wave on 787-9

Posted by notyad22@reddit | aviation | View on Reddit | 53 comments

Does this look like air pressure waves on the wing to you? It looked like it was casting shadows and moving across the wing. We were flying straight and level as well.

I have never seen something like this in real life before so I don’t know if my eyes were getting tricked. I also moved my phone around to try and see if it was some sort of reflection.

This is the best video I could get to capture it. Below are the references I could gather from flight data onboard.

40000 ft True airspeed 561 mph Ground 510 -74 F Headwind 43mph

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rinfodiv@reddit

Congrats, you found the shock wave! Even subsonic planes you have -some- transonic airflow.

But uh… why is it green?

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notyad22@reddit (OP)

The windows had no shades so you could change the tinting and darkness of them. To my eyes it was clear but on camera it looks green for some reason

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volodymyroquai@reddit

Is that the Dreamliner? I bloody hate their windows.

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Likewise. Was so stoked to finally fly on one... until we experienced the windows. Had to tape the airplane safety card over the window because the sunrise was right on the baby's face while sleeping and even on full dark it was disturbing him. The electronic shades also don't block the heat of the sun either, which of course is much more intense in the thinner atmosphere. Thankfully the crew didn't lock out our controls so we had clear views when we did want them.

Give me physical blinds any day, sad to say.

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volodymyroquai@reddit

I flew from Haneda to Heathrow ...over Alaska and Greenland.

14 hours of sunlight beaming on my face when my body thinks it's 01:00 by the time it takes off.

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pmcclay@reddit

ooh. I guess I haven't been flying much in a while...

Does that mean the crew can just un-dark all the shades for landing instead of doing the announcement and row-by-row cajoling?

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dr_stre@reddit

They can and they do.

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WWYDWYOWAPL@reddit

It’s obnoxious when they make all the windows dark on long flights. Like I paid for a window seat, I wanna look at the clouds damnit.

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pmcclay@reddit

I guess it makes sense to darken the windows instead of the general announcement to 'please consider as a courtesy to your neighbors who would rather fast-forward to breakfast', but then are you really prevented from un-darkening your own window? That would indeed be pretty sad.

(yes I could just ask google but for the sake of the conversation...)

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smokie12@reddit

I feel like it should be possible to force them all dark and then just release the lock, so anyone that wants to adjust can do so?

I mean I'd be pissed if my seat neighbor wanted to burn their eyeballs out with a full bright window in an otherwise pitch black plane, but surely one notch above pitch black should be okay?

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DeletedByAuthor@reddit

If you've got the window seat it's in your control, your neighbor can beat it if they don't like it lmao. You literally pay for the convenience of having the lever, don't let them pressure you into settling for anything less than you booked lmao.

If you can't handle the lights get a sleeping mask, that's what they're for.

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Any-Vehicle4418@reddit

Yes crew can override

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notyad22@reddit (OP)

Here’s a picture of a slightly lighter setting on the windows

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Tupcek@reddit

this isn’t window setting, you were just flying over Mexico

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HF_Martini6@reddit

It's called electro-chromatic or smart glass and more or less uses the same effect as LC-Displays (in layman’s terms)

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Aggressive_Let2085@reddit

The 787 has tinted window shades instead of the normal covers

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InnerBreath2884@reddit

So much fancier!

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squeeby@reddit

They’re not supposed to be yellow though. I’ve flown on several 787s that had one entire side of yellow windows when not “dimmed”.

Apparently (according to another reddit source I can’t find at the moment) it’s to do with the effect the sun has on the chemical that provides the shade function.

The flights that run to the same destinations regularly have the sun on same side so only one side gets affected.

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NoDoze-@reddit

I can't tell if its the window or glare, or actually outside on the wing.

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LazyGit@reddit

Apologies if I'm wrong but I believe this isn't so much the shockwave itself but the shadow of the shockwave.

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Playful-Painting-527@reddit

The shockwave causes an increase in pressure and thus an increase in density. What you are seeing is a refraction in the air due to the density gradient.

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LazyGit@reddit

I'm pretty sure it's the sun shadowgram of the transonic shockwave. I don't see any refraction in this video.

You can see the shadow and the refraction in this video however: https://www.youtube.com/watch?v=icLNtF_ehwo

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Trick-Ad-4550@reddit

Pretty common on pretty much every jet to have shockwave somewhere on top of the wing during cruise.

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punkslaot@reddit

The hell are you looking at?

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Same_Ambassador_5780@reddit

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Background-Taro-573@reddit

I thought I was colorblind, looking for the blue circle 🙃

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punkslaot@reddit

That looks like something in the window

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Variabell556@reddit

Yeah I legitimately thought my phone screen just wasn't clear enough for me to see what everyone is talking about. I thought that was obviously a reflection in the window

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kelby810@reddit

Its not a reflection. The OP moves their camera all over the window and the shock doesn't change location.

Its a well known phenomenon that I've personally seen in flight -- this looks the same to me. Its hard to capture on a camera but its unmistakable in person, similar to heat blur, but only a thin slice of it.

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yeahgoestheusername@reddit

Thanks for the help. That’s cool!

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Same_Ambassador_5780@reddit

I tried to post a screenshot pointing out the shockwave but for some reason, it won't post.

There's a long, thin shadow moving back on and forth ever so slightly on the wing. The shadow is caused by light refraction as it passes through the shock wave.

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yeahgoestheusername@reddit

My thoughts exactly

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Spin737@reddit

Light/dark line from bottom right to top left. Dances a bit. I look for them when I’m in the overwing seats.

Looks almost like cellophane tape being suspended.

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P0t4t0g0d@reddit

Wow, that's the cleanest I've seen sofar

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InevitableFly@reddit

Ive never seen one before but doing a quick google, it looks like a shock wave

Another reference I found to a picture of the same thing

https://commons.wikimedia.org/wiki/File:Shock_wave_above_airliner_wing_%281%29.jpg

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REpassword@reddit

What are you looking at in the photos?

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26635785548498061381@reddit

It's really subtle, so zoom right in and look towards the bottom of the red line. Just above it, there is a small ripple, looks even just like some extra paint, running the length of the wing. It's that.

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REpassword@reddit

These subtle arcs?

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26635785548498061381@reddit

Yep, exactly.

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REpassword@reddit

Thank you! Very interesting.

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Regal_Name@reddit

i studied about this last month. critical mach number or mcrit speed where airspeed around parts of the plane has reached mach 1. mcrit is a pre defined number given by the manufacturer, it is advised to be cautious around these speeds.

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