Seems like a perfectly reasonable test to me?

This proves that an engine can run on this fuel at 100% concentration. The other engine is exactly the same, there's no reason that this result doesn't carry over to a flight with /both/ engines using this new fuel. This is just a safer test if there turned out to be problems with the experimental fuel.

The article mentions this in the very first paragraph, I don't think there's anything to complain about here.

I also don't think the headline is misleading either. The important thing being tested here is that the engine managed a flight with a 100% concentration of the new fuel, the other engine being a failsafe with known safe fuel doesn't make the outcome of the test any less useful.

Edit: the headline on the page mentions the second engine using legacy fuel, I'm not sure why the HN headline was modified.

It is a smart way to test. If it doesn't work, you still have another engine backed by roughly a century of experience.

EDIT:

My horrible, ostentatioous BAD! I mixed up the GE headline with the viral United Airlines tweet about the same exercise:

https://twitter.com/united/status/1466045020473942020

In which they took care not to mention the second engine using standard fuel, going so far as to say (this time quoting correctly):

  Today, United will be the first in aviation history to fly a passenger flight using 100% sustainable aviation fuel (SAF).  

  This flight will serve as a turning point in the industry's effort to combat climate change.

So I definitely should have read the GE headline more closely (which doesn't make this obfuscation). But that's what happens when these companies keep lying, and lying, and lying - at some point your senses go numb, your eyes start to bleed... and you lose track of detail.

But at the end of the day - my bad!

Earlier, ill-thought transmission (from me) follows below, as-is:

  The point isn't the testing protocol, or that two different fuel types were used.

  It's that these companies are trying to play with our heads.

A 50% reduction in the emissions associated with flying, with no additional changes to the infrastructure involved is a game changer. If we can do this for planes, then ships and trains aren't far off.

Yup - that's exactly the take-away they would like the reader to have.

But (as noted in the article I linked to), apparently has significant scalability issues, and (because of sourcing and transport issues) is not "100 percent" emissions-free.

So? Something is better than nothing.

But it's not a ... "game changer".

It would probably fly if it were in both engines, yeah?

The modern media is at fault here, not nessecarily the company.

The linked article is a press release from GE, the engine manufacturer, and its headline says 'in one engine' clear as day.

Do you mean the HN headline? As far as I can see, that's the source of consternation.

A little unfair to blame the company here, no? The fuel is 100% sustainable and it would be illegal to use more than 50% of it here

It's also unfair to blame the article. The actual press releases headline was correct and precise about this. The only place it got messed up was the HN headline.

Nothing about it being modern is relevant to them missing specific information here. That's happened for centuries. But I agree nonetheless, we shouldn't fault the company for having a fail-safe

... and?

If one engine works entirely fine on a 100% blend, with no ill effects in operation or in analysis afterwards (for weird deposits on the hot section), it's reasonable to conclude that one could run exclusively on it.

There's a chunk of wisdom over in experimental aviation (the "You can build and fly whatever you want, please try not to kill anyone else in the process..." side of things): "Never test an experimental engine on an experimental airframe." If you're building a new airframe, use a proven engine. If you're trying a new engine, use a proven airframe. Otherwise you just end up with an explosion of possible issues, and "experimental engine plus experimental airframe" tends to lead to an alarmingly short lifespan.

Running one engine on an experimental fuel, while keeping the other on something you know is entirely sane and will work fine, is entirely reasonable. You know the airplane can fly and land safely on one. You think the other one works fine - but there are some weird corner cases in aviation - British Airways Flight 38 was one of those things. In this particular, exceedingly difficult to reproduce case, water in the fuel iced up and clogged the fuel flow to both engines, leading to a crash short of the runway (no fatalities, mostly due to the skill of the pilots). The engines behaved absolutely fine, until short final, at which point they suddenly, and without any prior warning, refused to make power - because they couldn't get enough fuel.

The entire point of testing is to work out as much of this sort of stuff as you can. If it turns out that after cruise, you've got weird fuel icing issues, it is far better to have that problem limited to one engine, where the other one can pick up the slack and haul you into a goaround if needed (twinjets are typically obscenely overpowered on two, because they need to perform well with an engine out).

Doing it the way United did is entirely sane, reasonable, and rational for any sort of aviation testing. Doing it on both engines, without serious testing beforehand (of the "on one side" variety), would be insane in aviation.

Ok, we've put one engine in the title above.

The article title doesn't have this issue because it clearly says "Supplying One Of Its Engines". I wonder if they added after getting criticized or if it was there all along. Edit: probably the former, since the original press release omitted it: https://www.prnewswire.com/news-releases/united-to-become-fi.... Pretty silly to think they could get away with that.

I assume that this rule will change once SAF builds up a long-term track record of safety and reliability.

EV batteries started this way with hybrids like the Prius. Look where we are.

Actually Priuses use a completely different battery tech than EVs like Tesla.

True. The point was that there’s a progression in the technology. Nickel Cadmium -> Lithium Ion -> ?Solid State. More importantly, there’s the cost curve improvement.

True for pure hybrid Priuses, but Plug-in Priuses use Lithium-Ion batteries just like Teslas.

Yes, misleading headline for sure. But as a testing strategy it certainly makes sense.

The point is that the "headline" doesn't come from a news outlet.

But from the company pushing the product.

Unless they changed it, the headline on the page is:

"United Flies World’s First Passenger Flight On 100% Sustainable Aviation Fuel Supplying One Of Its Engines"

And it's in the url too.

The latter seems better to me.

So the FAA should change the regulation on the maximum concentration of SAF?

I am not sure the GP caught the article's statement that the regulatory cap on SAF is 50%, and that as a result this is arguably the most aggressive test UA could have run.

Article headline:

> United Flies World’s First Passenger Flight On 100% Sustainable Aviation Fuel Supplying One Of Its Engines

Third sentence:

> It was the first commercial flight with passengers on board to use 100% drop-in sustainable aviation fuel (SAF) for one of the aircraft’s two engines.

I read it as meaning the fuel was 100% sustainable.

Turns out it that's not true either. See the article linked to in my post.

Well, who expects complete honesty in a marketing press release anyway?