Highly Asymmetric Trail with No Gap by Engine

[marko.posavec]

(Hope this is the proper place to post this)

British Airways 777 leaving a strange contrail yesterday afternoon. It's not the absence of the other trail that bothers me (it's shadowed by the aircraft, just like half of the left-side contrail), what's weird (I think) is the place where the trail begins. There is no gap between the engine and the trail, almost as if the trail starts before the actual exhaust.

Photo was taken July 28, 2023 at 15:20 UTC.
Camera: Nikon D500, Sky-Watcher Maksutov 127/1500
Flight:
British Airways Boeing 777 Mumbai - London as flight BA198
Altitude 36.000 feet, external temperature as reported by Flightradar24 -51°C

Photo is a bit out of focus. I'm trying to recover some more from the card which I already formatted... I wrote them off and only later realized there's something curious about the trail.

Look where the engine #1 trail begins:

Unsharp masked:

A wider view, showing faintly the other contrail and the other part of the curious one. So there:

Unsharp masked #2:

 

[Mick West]

If it wasn't for the single bright streak by the engine, I'd say it looks like a normal exhaust contrail on a plane roughly facing the sun, so most of the contrail is in shadow.

The white streak is a little mixed up with the flap fairing. Here's the sun position, coming from ahead and to the pilot's left.

(Plane is flying NW, the thin line ending at the pin. The sun is the thick yellow line. 30° Altitude, 266° Azimuth

Seems like one of

1. An aerodynamic contrail coming from part of the engine structure
2. A regular exhaust contrail that's starting super early.
3. Something (water?) draining from the engine
4. Smoke from the engine.

More photos would be useful. Or other examples of something similar.

 

[Mick West]

From this old article I wrote:

Article:

One more thing that can affect the apparent gap is how it is illuminated by the sun. Contrails don't just spring into existence as solid white clouds, they start out quite faint and transparent. If this region is lit by direct sunlight, then it's more visible, and the gap will seem shorter. If it's not lit by the sun – like if the plane is in the shadow of a cloud, then the gap will seem longer.
The following photo illustrates this. The contrail on the left of the photo is being shaded by the body of the plane. Even though both contrails are the same behind the plane, meaning they have the same short gap, the gap on the left contrail looks much longer.

Source: https://contrailscience.com/how-big-is-the-gap-between-contrails-and-engines/

 

[Mick West]

While looking for examples, I saw this interesting video, whigh seems like puffs of stronger contrail were coming from one engine. Possibly caused by an increase in particulates.

Source: https://www.youtube.com/watch?v=3g16cPkkN_c


More photos would tell us if the streak was a transient puff like this, or a more sustained trail.

 

[Scaramanga]

There's nothing remotely unusual about it. Sometimes the difference between layers of air that have different dew points and thus affect the production of contrails can be a few feet....both laterally and vertically. This is why one sometimes gets contrails looking like morse code, with gaps and breaks....even with the aircraft maintaining height....as waves within the atmosphere make the plane alternately pass through higher and lower dew points. It's all pretty standard stuff.....though 'chemtrail' advocates love to misdirect and confuse over what is basically everyday meteorology that they don't understand.

 

[Mick West]

There's nothing remotely unusual about it. Sometimes the difference between layers of air that have different dew points and thus affect the production of contrails can be a few feet....both laterally and vertically. This is why one sometimes gets contrails looking like morse code, with gaps and breaks....even with the aircraft maintaining height....as waves within the atmosphere make the plane alternately pass through higher and lower dew points. It's all pretty standard stuff.....though 'chemtrail' advocates love to misdirect and confuse over what is basically everyday meteorology that they don't understand.

I disagree. It's unusual if we can't find other examples. It's a 777. I've been unable to find a contrail that seemingly touches the engine like that.

 

[Scaramanga]

what's weird (I think) is the place where the trail begins. There is no gap between the engine and the trail, almost as if the trail starts before the actual exhaust.

That is air that bypasses the engine and is not actually 'the exhaust'. It is how turbofan engines work. That bypass air will also have been compressed to some degree....and it can create a trail due to rapid decompression in leaving the engine bypass.

 

[Scaramanga]

I've been unable to find a contrail that seemingly touches the engine like that.

It's coming from the turbofan bypass. This air is compressed but not fuel injected or significantly heated. The regular exhaust needs to cool a little before creating a contrail, but the bypass air was never heated to that degree in the first place so can create a contrail immediately at the engine. I'm guessing this would be mostly due to rapid depressurization. Even the wings can produce short contrails under the right conditions....which most of us have seen when flying.

 

[Mick West]

That is air that bypasses the engine and is not actually 'the exhaust'. It is how turbofan engines work. That bypass air will also have been compressed to some degree....and it can create a trail due to rapid decompression in leaving the engine bypass.

Do you have an example of this? Aerodynamic contrails commonly form over the wings. More defined ones can come from wingtip vortices. I don't recall seeing one from bypass air, or under the wing.

 

[Scaramanga]

Do you have an example of this?

I haven't seen any examples...but the engine turbofan bypass ( which is in front of and to the side of the exhaust nozzle ) is clearly the area that the trail is coming from in the first OP picture. Any search for 'turbofan bypass contrail' brings up almost nothing. Most photos of contrails simply aren't close enough to resolve into bypass or main nozzle...and the nearest I could get was this, which shows some element of contrail not coming directly from the nozzle exhaust.

Incidentally, the bypass only exists in turbofan engines ( which the Boeing 777 uses ) ....and not on turboprop or turbojet engines. Which is why you would not in any case see bypass contrail on every jet.

 

[Trailspotter]

I think that the white streak across the wing is not necessarily due to condensation, but can be just an optical effect - a scattering or refraction of light on the hot exhaust made visible on a changing background. Somewhat similar to what I saw for a jet airliner passing in the front of a contrail:

Source: https://youtu.be/jMLv602-2JQ?t=31

or the edge of the Moon:

Source: https://youtu.be/HC7rBqoMTE8?t=27

 

[Scaramanga]

(Hope this is the proper place to post this)

British Airways 777 leaving a strange contrail yesterday afternoon. It's not the absence of the other trail that bothers me (it's shadowed by the aircraft, just like half of the left-side contrail), what's weird (I think) is the place where the trail begins. There is no gap between the engine and the trail, almost as if the trail starts before the actual exhaust.

Photo was taken July 28, 2023 at 15:20 UTC.
Camera: Nikon D500, Sky-Watcher Maksutov 127/1500
Flight:
British Airways Boeing 777 Mumbai - London as flight BA198
Altitude 36.000 feet, external temperature as reported by Flightradar24 -51°C

Photo is a bit out of focus. I'm trying to recover some more from the card which I already formatted... I wrote them off and only later realized there's something curious about the trail.

Look where the engine #1 trail begins:

View attachment 60756

Unsharp masked:

View attachment 60757

A wider view, showing faintly the other contrail and the other part of the curious one. So there:

View attachment 60758

Unsharp masked #2:

View attachment 60759

Now that I look at it closely, there is something wrong with this picture. Contrast the left and right engines. The right engine looks fine, but the left engine looks badly mis-shapen....the rear engine cowling is much smaller than the right engine, and it appears some of the lower part of the left engine is simply missing. I'm no good at doing overlays but someone might want to overlay them and see the big difference. Given this mis-shapen and distorted-ness....its likely the contrail is part of that too.

 

[cptreynolds]

Now that I look at it closely, there is something wrong with this picture. Contrast the left and right engines. The right engine looks fine, but the left engine looks badly mis-shapen....the rear engine cowling is much smaller than the right engine, and it appears some of the lower part of the left engine is simply missing. I'm no good at doing overlays but someone might want to overlay them and see the big difference. Given this mis-shapen and distorted-ness....its likely the contrail is part of that too.

The engine cowlings are fitted with a strake (small wing-like surface) on their inboard upper side. Looking from off center below the aircraft, they're expected to look asymmetric. The bulge on the left engine is that strake. Not sure if that helps though.

 

[cptreynolds]

(Hope this is the proper place to post this)

British Airways 777 leaving a strange contrail yesterday afternoon. It's not the absence of the other trail that bothers me (it's shadowed by the aircraft, just like half of the left-side contrail), what's weird (I think) is the place where the trail begins. There is no gap between the engine and the trail, almost as if the trail starts before the actual exhaust.

Photo was taken July 28, 2023 at 15:20 UTC.
Camera: Nikon D500, Sky-Watcher Maksutov 127/1500
Flight:
British Airways Boeing 777 Mumbai - London as flight BA198
Altitude 36.000 feet, external temperature as reported by Flightradar24 -51°C

Photo is a bit out of focus. I'm trying to recover some more from the card which I already formatted... I wrote them off and only later realized there's something curious about the trail.

Look where the engine #1 trail begins:

View attachment 60756

Unsharp masked:

View attachment 60757

A wider view, showing faintly the other contrail and the other part of the curious one. So there:

View attachment 60758

Unsharp masked #2:

View attachment 60759

I would suggest asking over at aviation.stackexchange.com by the way. Happy to crosspost for you if you want.

 

[DavidB66]

Now that I look at it closely, there is something wrong with this picture. Contrast the left and right engines

I thought they looked odd too, but I was reluctant to expose my ignorance by saying so. In the large photo at #12 above there appears to be a structure attached to the wing just adjoining the 'right hand' engine on the side of the engine furthest from the fuselage. By symmetry, one would expect the corresponding structure on the 'left hand' engine also to be on the side of that engine furthest from the fuselage, but in the photo it looks as if it is on the side closest to the fuselage. This can hardly be the actual physical state of the aircraft (someone would have
noticed!), so I assume it is some trick of perspective or lighting. Either that or there is something wrong with the photograph itself.

[Note: I did try to find photos online which clearly show the position of these 'structures' (which I think are called pylons) but I found it remarkably difficult.]

 

[Trailspotter]

I thought they looked odd too, but I was reluctant to expose my ignorance by saying so. In the large photo at #12 above there appears to be a structure attached to the wing just adjoining the 'right hand' engine on the side of the engine furthest from the fuselage. By symmetry, one would expect the corresponding structure on the 'left hand' engine also to be on the side of that engine furthest from the fuselage, but in the photo it looks as if it is on the side closest to the fuselage. This can hardly be the actual physical state of the aircraft (someone would have
noticed!), so I assume it is some trick of perspective or lighting. Either that or there is something wrong with the photograph itself.

[Note: I did try to find photos online which clearly show the position of these 'structures' (which I think are called pylons) but I found it remarkably difficult.]

There is nothing wrong with the photo. The pylons are connected to the top of the engine nacelles along their centrelines. As we see them at a (small) angle, they are both on the same side of the engines.

As already noted,

The engine cowlings are fitted with a strake (small wing-like surface) on their inboard upper side. Looking from off center below the aircraft, they're expected to look asymmetric. The bulge on the left engine is that strake. Not sure if that helps though.

The engine nacelle strakes, a.k.a., nacelle chines, can produce aerodynamic contrails, which are usually occur near the ground and, because the engines are placed ahead of the wing, go over the wing, which is not the case here.

Source: https://youtu.be/BH7FujP9iXk

 

[Scaramanga]

The engine cowlings are fitted with a strake (small wing-like surface) on their inboard upper side. Looking from off center below the aircraft, they're expected to look asymmetric. The bulge on the left engine is that strake. Not sure if that helps though.

No, I don't accept that explanation. We are viewing two engines 70 feet apart....at a distance of 36,000 feet plus additional feet for the plane being at an angle. Call it 40,000 feet.

That means the difference in viewing angle between the two engines is a mere 1/10 of a degree ( one degree is 700 feet ). On the engine itself ( which is conveniently circular for such purposes ) that corresponds ( on an 11 foot wide engine ) to 0.23 inches around the circumference of the engine. That should not totally change the shape and size of the cowling ( look at the blue cowling at the rear of both engines ) even if there are assymetric strakes. Look at the rear of the cowlings in the magnified version I posted.....they are completely different widths.

At that distance and with the tiny viewing angle variation, the two engines should appear practically identical. Here's the two engines right next to each other for comparison....there isn't a tiny difference, there's a huge difference.

 

[cptreynolds]

I thought they looked odd too, but I was reluctant to expose my ignorance by saying so. In the large photo at #12 above there appears to be a structure attached to the wing just adjoining the 'right hand' engine on the side of the engine furthest from the fuselage. By symmetry, one would expect the corresponding structure on the 'left hand' engine also to be on the side of that engine furthest from the fuselage, but in the photo it looks as if it is on the side closest to the fuselage. This can hardly be the actual physical state of the aircraft (someone would have
noticed!), so I assume it is some trick of perspective or lighting. Either that or there is something wrong with the photograph itself.

[Note: I did try to find photos online which clearly show the position of these 'structures' (which I think are called pylons) but I found it remarkably difficult.]

There's a flap track fairing (these structures at the rear/"trailing edge" of the wing) each inboard and outboard of the engine attachment. On the side with the spurious contrail, one fairing is hidden behind that contrail.

I have to say, both wings and engines look fairly normal to me, albeit a bit skewed, but I'll attribute that to telephoto compression).

Can't look it up at the moment - did the flight reach its destination (in which case this venting probably didn't cause much concern on the flight deck)?

 

[Trailspotter]

No, I don't accept that explanation. We are viewing two engines 70 feet apart....at a distance of 36,000 feet plus additional feet for the plane being at an angle. Call it 40,000 feet.

That means the difference in viewing angle between the two engines is a mere 1/10 of a degree ( one degree is 700 feet ). On the engine itself ( which is conveniently circular for such purposes ) that corresponds ( on an 11 foot wide engine ) to 0.23 inches around the circumference of the engine. That should not totally change the shape and size of the cowling ( look at the blue cowling at the rear of both engines ) even if there are assymetric strakes. Look at the rear of the cowlings in the magnified version I posted.....they are completely different widths.

At that distance and with the tiny viewing angle variation, the two engines should appear practically identical.

The engine nacelles of Boeing 777 are not perfectly circular:

 

[cptreynolds]

No, I don't accept that explanation. We are viewing two engines 70 feet apart....at a distance of 36,000 feet plus additional feet for the plane being at an angle. Call it 40,000 feet.

That means the difference in viewing angle between the two engines is a mere 1/10 of a degree ( one degree is 700 feet ). On the engine itself ( which is conveniently circular for such purposes ) that corresponds ( on an 11 foot wide engine ) to 0.23 inches around the circumference of the engine. That should not totally change the shape and size of the cowling ( look at the blue cowling at the rear of both engines ) even if there are assymetric strakes. Look at the rear of the cowlings in the magnified version I posted.....they are completely different widths.

At that distance and with the tiny viewing angle variation, the two engines should appear practically identical. the light on the lower side of the left engine blurs its shape into the sky?

Ok. But is it possible it just seems that way with the illuminated lower left hand side of the left engine blurring its silhouette into the sky?

 

[cptreynolds]

The engine nacelles of Boeing 777 are not perfectly circular:

View attachment 60780

Are you sure it's the correct 777 version? You need a -300ER to prove the point (which was the first variant where you couldn't choose the engine when buying the plane).

 

[Scaramanga]

The engine nacelles of Boeing 777 are not perfectly circular:

I think you are ignoring or simply not looking at the point I am making. Why are the rear engine cowlings two completely different widths in the side by side example I gave ? It could not be more blatantly apparent. Why is the upper part of one of those rear cowlings completely missing ?

 

[JMartJr]

Is the bit that appears to be missing a discrete bit that could,say, fall off as a unit?

 

[Trailspotter]

I think you are ignoring or simply not looking at the point I am making. Why are the rear engine cowlings two completely different widths in the side by side example I gave ? It could not be more blatantly apparent. Why is the upper part of one of those rear cowlings completely missing ?

Firstly, I commented on your post before you added the last sentence and a comparison collage.
Secondly, I do not think that "the upper part of one of those rear cowlings completely missing". There seems to be a patch of reflected light on it.

The aircraft in question is Boeing 777-336ER G-STBF. Here is one of its many photos:
https://www.jetphotos.com/photo/10778774

Edit: It appears that the engine nacelles do not have to look identical (i.e., symmetrical). I found an older photo of the same plane with two engine nacelles looking rather different:
https://www.planespotters.net/photo/1390708/g-stbf-british-airways-boeing-777-336er

 

[cptreynolds]

Firstly, I commented on your post before you added the last sentence and a comparison collage.
Secondly, I do not think that "the upper part of one of those rear cowlings completely missing". There seems to be a patch of reflected light on it.

The aircraft in question is Boeing 777-336ER G-STBF. Here is one of its many photos:
https://www.jetphotos.com/photo/10778774

Edit: It appears that the engine nacelles do not have to be identical (i.e., symmetrical). I found an older photo of the same plane with two engine nacelles looking rather different:
https://www.planespotters.net/photo/1390708/g-stbf-british-airways-boeing-777-336er

If you use this from the other side, the effect remains the same, showing that it's ok if it's asymmetric.

https://www.planespotters.net/photo/1089360/g-stbf-british-airways-boeing-777-336er

 

[Trailspotter]

Here is a 2019 photo of the same aircraft (G-STBF Boeing 777-336(ER) of British Airways) in a similar orientation to the original, but in a much better resolution:

Source: https://www.facebook.com/photo/?fbid=2333735153525704&set=pcb.2333736460192240

 

[marko.posavec]

Unfortunately, the other photos are unrecoverable. I should have noticed the odd trail sooner...

As for the difference in appearance of the engines, there's a lot of air between me and the plane and it's really common to have noticeable distortions on parts of the aircraft. My scope has a small aperture and is not quite suited for this type of photography.

The bypass explanation seems plausible. I'm digging through my older 777 photos to see if I can find something similar.

Post-processing was contrast enhancement, noise reduction and sharpening. Nothing else. It's a poor image and I would have discarded it if not for the interesting contrail.

 

[DavidB66]

Here is a 2019 photo of the same aircraft (G-STBF Boeing 777-336(ER) of British Airways) in a similar orientation to the original, but in a much better resolution:

Source: https://www.facebook.com/photo/?fbid=2333735153525704&set=pcb.2333736460192240

Thanks. I think that resolves the discrepancy that worried me. The structures behind the engines are symmetrical, so from the viewpoint of the original photos different parts of the two structures would look very similar.

 

[Mick West]

Unfortunately, the other photos are unrecoverable. I should have noticed the odd trail sooner...

Could you zip and upload the original image, as raw as possible?

 

[marko.posavec]

Sure. Here's the original .NEF file: https://www.dropbox.com/scl/fi/vtgl...6974.zip?rlkey=0z1adhd4ccp33cpituol4fe30&dl=0

 

[cptreynolds]

I would suggest asking over at aviation.stackexchange.com by the way. Happy to crosspost for you if you want.

Reiterating my suggestion to ask about the venting at aviation.stackexchange.com (my post may have been overlooked as moderation took a while, I'm new after all). It'll be answered quite quickly over there I believe.

 

[marko.posavec]

Reiterating my suggestion to ask about the venting at aviation.stackexchange.com (my post may have been overlooked as moderation took a while, I'm new after all). It'll be answered quite quickly over there I believe.

You're right, I did miss that suggestion. Of course, absolutely, feel free to crosspost over there.

 

[cptreynolds]

You're right, I did miss that suggestion. Of course, absolutely, feel free to crosspost over there.

Phantastic, thanks. Done:

https://aviation.stackexchange.com/...ing-from-left-engine-outboard-side-what-is-it

 

[Mick West]

Sure. Here's the original .NEF file: https://www.dropbox.com/scl/fi/vtgl...6974.zip?rlkey=0z1adhd4ccp33cpituol4fe30&dl=0

Thanks, other than the swarm of UFOs, I'm not sure if there's more there. Maybe a little more clarity on where the trails starts.

 

[cptreynolds]

First response on https://aviation.stackexchange.com/...ing-from-left-engine-outboard-side-what-is-it by John K. contains

Well, it's not condensate water from the tail pipe, and it looks to be originating from the main cowl, so it can only be one of the Big Three fluids; fuel, engine oil, or hydraulic oil (for the reversers, assuming they're hydraulically driven). Such leaks are not unheard of.