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, ther

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.