Contrails: How tweaking flight plans can help the climate.

[a1anx]

From The BBC " Contrails: How tweaking flight plans can help the climate." IMHO this looks like a non starter but what do I know.

https://www.bbc.co.uk/news/business-58769351.amp

[wiggy]

Worthy effort I’m sure, and something worth considering, something must be done etc… but when you read:

“Prof Hayward says the next challenge is for airlines to work out how altitude changes of a "few thousand feet" can be made mid-flight to avoid contrails while also not disrupting passengers' comfort. A pilot would need to spot these in "sufficient time for an aircraft to adapt gracefully", he adds.”

You realise that this is yet another area where some of the researchers, ever willing to comment, have perhaps had little if any exposure to operational flying.

Neve mind upsetting the G&T, I think more of a challenge might be how these “few thousand feet” altitude changes are going to be facilitated for presumably multiple aircraft in busy RVSM airspace…

(BTW and as a FWIW umpteen decades back some Met forecasts included/details the minimum contrail/ “Mintra” levels/altitudes, I guess now there’s the ability to do it much more accurately than in days of old).

[B2N2]

Personally….I think passenger comfort is overrated.
People do NOT book airline tickets based on smoothness, they only look at cost despite the best efforts at virtue signaling and corporate branding.
No-contrail flying definitely worth looking into.

[cattletruck]

Been reading the annual report of a met agency and how many millions of dollars they have value added to the aviation industry by helping them save tens of millions of litres of fuel by providing them with enough information for choosing favourable flying altitudes. Methinks the good professor should stand back a little and look at the big picture.

[switch_on_lofty]

Lots of routes I fly in Europe e.g UK to Canaries or over Austria/N Italy where there is a lot of traffic there are often high level clouds caused by so many planes making persistent contrails. A way of reducing these would definitely be beneficial from a climate perspective.
Operational challenges: given most flights I fly we go as high as possible for efficiency generally. Flying higher isn't normally an option, flying lower will generally increase fuel burn. Which may be of more climate benefit if it prevents enduring contrails despite higher CO2.
But then you'd either need to carry more fuel all the time = higher fuel burn or just on some flights when it's possible.
Looking at a rear facing camera and adjusting sounds nice but isn't too realistic.
Disclaimer yes I know that relative headwind/tailwind can sometimes exceed benefit of climbing.

[OldLurker]

Forgive an ignorant question from humble SLF, but isn't it normal to change altitude for optimum performance during cruise? For example, 4,000ft 'step climb' as fuel is used up? Pax never notice.

[RVF750]

Yes, it's normal. You tend to go up in 2,000ft increments. However, winds change aloft and sometimes your flight plan may well ask you to drop down 2,000ft to take advantage of a jetstream for example. All I know is always looking to go higher works mostly, but it does pay to look at the upper winds first. Sometimes you are given lower levels to avoid slots and restrictions on a part of the route, which in reality are not needed. other times it's for weather and helps a lot. Just being aware and paying attention can make the difference. Not that managers will ever credit you for doing it..

[a1anx]

I rarely take a news story at face value; particularly from the BBC. This is probably a tentative opening shot in a campaign to severely restrict aviation in line with the zero net carbon thing.

[wiggy]

OldLurker

Yes it is, for the reasons RVF750 mentioned…on a long haul flight you may well step up (rarely down but it happens) several times during the cruise and as you say the pax hardly ever notice….

I hope the Prof on the article was making a slightly light hearted comment….from a practical POV it’s the handling of all traffic approaching a block of contrail prone airspace all wanting to step up/down to avoid that probably much much more of a real world problem.

[nonsense]

Most research starts at the level of "Is there an effect here?", not "What are the full implications of this effect and how shall we best exploit it?"

I don't think Wilbur and Orville envisioned moving 500 people at a time halfway around the world at 38,000 feet when they worked out that they could fly a few hundred feet just above some sand dunes in North Carolina.

The press, of course, like to spruik the most spectacular possible outcome when reporting really basic research. Outside of aviation, hydroxychloroquine in a petri dish comes to mind.

[RTO]

Soo, we should burn more fuel in order to not produce contrails? Seems legit....

[Nick 1]

Can you imagine the number of TCAS RA having this big mass of a/c changing level every second ? It remind me the circular runway solution …

[DaveReidUK]

Life, including aviation, is full of trade-offs.

[HOVIS]

The ICA thanks you for your service.
Dimmer skies for a brighter future. 😁

[SWBKCB]

RVF750

So there are already processes in place that safely allow a/c to fly at their 'optimal' altitude. If the effect can be predicted (i.e. what's the best altitude to reduce contrails), is it not just a case of using those processes but to now fly at what is the new 'optimal' altitude - having taken account of the trade offs...

[DogTailRed2]

You could save a lot of pollution and fuel by not flying fruit across the globe.
Do we really need Sharon Fruit, Cumquots, Kiwi fruit and the like (In Farnborough) flown from places like New Zealand (or whereever they come from).
Lets go back to home grown seasonal produce.

[wiggy]

SWBKCB

That’s great if you are the only aircraft in a block of sky…you get your optimum level.

What we already know is that in the real world with multiple flights operating RVSM (1000’ vertical separation) combined with quite possibly tight horizontal separation it’s often not possible for everybody to be at their optimum level because somebody adjacent will have already got it…now at worse you might only be a few thousand feet off your optimum so it’s hopefully not a major problem…

However now chuck in this new idea that involves avoiding the trail levels - which might (and this is one for a met person) be a block of airspace thousands of feet thick- and it’s IMHO going to get much much more difficult to manage.

Who goes above the block? who goes below? …What happens in a few hundred or thousand miles when the contrail levels change and everybody wants or needs to shift up or down to avoid? In busy areas (e.g. States/Europe/North Atlantic Tracks once they really busy again) is there actually enough volume available to sanitise an entire block of airspace to avoid contrails and also still have the required separation between traffic?

Not saying it can’t be done but at a first glance there’s probably a bit more to it than simply saying just avoid certain levels and then coming up with procedures to avoid uncomfortable climbs and descents….

[Ex FSO GRIFFO]

Did 'Concorde' leave a contrail at FL650 or whatever?

Or 'The Sled' at FL800 (?)

At least they would be the 'only' aircraft 'up there'.... apart from other military types of course...

[Bullethead]

I understand that contrails can sometimes form into wide cloud bands, I’ve seen it dozens of times over my career but the same amount of water vapor is still produced by any aircraft whether or not it leaves a contrail behind it.


https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/448x250/59c3ea21_af78_4b62_9415_7a1ee387587b_9b03345c2c26b2e20f16288 e2b1b853af402921f.gif

[DaveReidUK]

"Contrail cirrus" is the term used to refer to that phenomenon.

[DuncanDoenitz]

B2N2

Agreed. I don't know about the merits/demerits of the proposals but, speaking as an occasional long-haul sardine, some occasional gentle-to-moderate aero's would at least relieve the tedium.

[Alt Flieger]

Maybe I’m missing something but I would have thought contrail cirrus would contribute to cooling not warming.

[sonicbum]

Passengers DO look for comfort and a smooth flights as a good percentage usually feels somehow uncomfortable when flying, especially in rough weather conditions. Try and ask any of Your non aviation acquaintances if they’d rather fly from A to B 2 hours in a noisy and bumpy ATR ride or 2 hours in a smooth and quiet jet at high altitude above most of the convective weather, at least in winter time.

[Genghis the Engineer]

May I stick my head above the parapet as I am both a PhD qualified researcher in an allied area, and holder of a CPL; I've also been to many of the main conferences on this topic over the last few years - so have a better grasp of these issues than most (including possibly a better grasp than that of the author of that, actually quite good BBC article).

This issue is very real, and the author gets the perspective about right. At the moment aviation, globally, is responsible for around 2-3% of total CO2 emissions (and CO2 is responsible for around 70% of what most people call global warming). However the science that's emerged over the last 5 years indicates very strongly that aviation's true contribution to radiative forcing (the technical term for the mechanism that drives global warming, and thus climate change) is around treble what we thought - nearer 7%, with much of the gap being caused by contrails cirrus - that is persistent contrails.

Contrail cirrus' mechanism is pretty straightforward - it's the same mechanism that makes cloudless days warmer, and cloudless nights colder - and vice-versa. Depending upon time of day either it's either reflecting radiation back into space, or reflecting it back into the earth (okay, it's always doing both, but the critical value is the net radiation transmission. The clever people who model this stuff (particularly a Prof Keith Shine at the University of Reading along with his colleague Dr Lucy Irvine, who for some reason never got mentioned in that article) have concluded that through the daily cycle, this all adds up to net warming, and thus is a big problem.

Now some other significant aspects. Contrails, which are caused by sooty particles in exhaust causing supercooled water vapour to precipitate upon those particles into ice crystals. It's not, as is widely misunderstood, caused by water in the exhaust. Persistent contrails occur in around 3% of air transport flying hours only, and they can only occur in air that is supersaturated with respect to ice.

So to eliminate contrails, we need to understand where (in 3D + time) the ice-supersaturated air is, and steer traffic over, under, or around it. That should be around 3% of flights, but it requires a particular form of weather forecast we don't presently have, and an integration of air traffic management and meteorology which we just don't have at the moment. These are solvable problems, but not quickly, cheaply or easily. The Germans have done some initial trials (almost entirely in German airspace) over the last couple of years, and hit many snags - they need to iron those out, but then we really need to do it on a much bigger scale over, e.g. the North Atlantic and Pacific.

The maths justifying this is really easy from a climate viewpoint. Re-route around 3% of flights, adding about 10% to each of their fuel burn - that puts aviation's CO2 emissions up around a third of a percent. For that you better than halve the real climate impact, through eliminating contrail cirrus and the warming effect that creates. My maths here is very crude, but you get the idea.

So if we can do it, we should. But it will require a massive upgrade of global met/ATM integration, much better testing of the standard equations for contrail creation and persistence than we presently have (my meteorology colleagues love to glibly quote those equations as gospel, and they are good, but the reality is they need somewhat more fine tuning than they've already had), some form of legislative or financial structure to ensure that aircraft genuinely do avoid ice-supersaturated regions as well as possible, and monitoring capability, probably space based, to confirm that persistent contrails aren't being formed.

I'd also personally like to see a reasonable proportion of airliners carrying some form of instrumentation that measures ice-supersaturation (and that's not at all trivial to do), most likely transmitting the measurements back to ATC and other aircraft in real time through spare ADSB-out capacity. That would be really useful in enabling this to work well, not to mention improving understanding of global meteorology, to absolutely everybody's benefit.

Very happy to discuss more if anybody's interested.

[B2N2]

Thanks for the explanation.

[cattletruck]

Depending upon time of day either it's either reflecting radiation back into space, or reflecting it back into the earth

Include urban sprawl, agricultural practices, and other deforestation activities in general which amplify the effect of absorbing and re-absorbing reflected radiation.

Although not used for detecting contrail conditions, there may be elements in this research which could prove to be useful.
https://ral.ucar.edu/solutions/products/algorithm-for-predicting-high-ice-water-content-areas-alpha

[B2N2]

sonicbum

You missed the point.
Pax won’t fly with you again if you’ve lost their luggage, they will fly with you again if it was a bumpy ride.
People don’t understand the logistics of luggage handling, they do somewhat understand you’re up in the air.

[sonicbum]

You’re mixing up different matters. Customers won’t come back or hardly will following a big disruption or a major issue ie. losing their luggage but that’s a common baseline for the industry.
Passengers are also looking for a cheap yet comfortable flight where they won’t spend a few hours in moderate turbulence because you need to reduce contrails.

[Alt Flieger]

Genghis the Engineer

Ok , I only have a humble BSc so I dont profess to be an expert but my reading of Global Warming theory is that the atmosphere is largely transparent to incoming radiation but enthusiastically absorbs longer wave radiation re-radiated from surfaces heated by incoming radiation.
Most of the return radiation is already absorbed by the existing mix of gases , most importantly H2O vapour. But there is not an infinite amount left to absorb. The idea that cirrus at over 30,000 ft can capture any residual radiation on the way out seems fanciful.
Like to see a reference to the original paper. Reading has a reputation of seeing Global Warming in everything.

[DaveReidUK]

The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018 (https://reader.elsevier.com/reader/sd/pii/S1352231020305689)

Looking forward to reading your rebuttal ...

[Genghis the Engineer]

Thanks for that paper Dave, I had missed its publication - that is a SERIOUSLY high powered author list and a really useful resource.

[Derfred]

Not a rebuttal, however the contrail effect is estimated at 57.4 out of a total 100.9 mW m−2.

But their estimated uncertainty range is actually somewhere between 17 and 98.

Furthermore, they have made a few of statements indicating how “uncertain” they are about their “uncertainty range”. Basically, there is very little data to support their model. For example, in Appendix E:
The statistical uncertainty of global contrail cirrus RF cannot be estimated from the small number of available studies. Uncertainties affecting our contrail cirrus estimates are, on the one hand, due to (A) uncertainties in the radiative response to the presence of contrail cirrus and, on the other hand, (B) uncertainties in the upper tropospheric water budget and the contrail cirrus scheme. In most cases, we can only infer very rough estimates for the uncertainties related to specific processes.