iirc, with better pictures they're now pretty sure it's an AL-31F. Remember what I said about SDF being overoptimistic?
And the text in the screenshot implies they are not Al-31.
Remember how when the first low-resolution image of J-20 came out, people said it is done in Photoshop? Then when high resolution images came out, people said the plane is a mockup? I specifically remember how one member claimed it is not physically possible to have all movable vertical tails, and then went into pseudoscience to justify his bias. Videos of J-20 being tested certainly shut him up for good and he was not seen posting again. But of course, other people started claiming the plane is for ground test only and cannot fly. When videos of the flight came out, they then claimed the plane is only a test demonstrator with no weapon bays. Guess what happened afterward?
I also remember that when 054A first appeared, there was a huge debate as to how many VLS cells it has. Due to the angle at which the pictures were taken, it was difficult to discern individual hatches. A lot of us argued that common sense dictates there should be 32 cells. One member argued that there were only 16 cells. This claim of course implied that the cells are rectangular. The member acknowledged it made no engineering sense whatsoever to have rectangular cells, but he maintained his claim anyway. Apparently, a claim that makes absolutely no sense makes more sense to him than Chinese defense industry not being incompetent.
So no, SDF isn't over optimistic. Rather, China is simply moving too fast than naysayers want to admit.
Like how AESA is slated for 2013 for J-10Bs with the depicted radar being PESA?
Having fielded many types of AESA radar already, why would China go backward for a PESA? There are even papers describing layout of elements for AESA, and the
. Furthermore, China is said to be developing AESA radar for JF-17. If China couldn't equip its own planes with AESA, why would it do so for Pakistan? These all support J-10B's radar being AESA.
If you take a strict interpretation of what's been said, all that means is that the J-20 should fly with some kind of indigenous engine this year. Even if the WS-10G and WS-15 are not ready, the Chinese should retain the option to fly the J-20s with Chinese engines so that the Russians can't use a kill code and the Chinese needn't be dependent on the Russians for aircraft production. It's just building in failsafes for a truly ambitious product.
The strict interpretation is that 4th generation first flight with domestic engines is top priority. The first flight of such an aircraft took place already, in January. So unless the J-20 isn't a 4th generation fighter, then the text means exactly J-20's first flight with domestic engines has occurred in January.
And as you've said, the first flight was in January. If it was one of the most important goals of the year, would it necessarily be crossed out at the start of the year? It's possible, yes, but I think it's unlikely. Of course, we can do all sorts of speculation of Chinese R&D processes; for example, you could say the Chinese are extremely well-prepared (then why is the J-10B still running on WS-10A not WS-10B or G?) and they got the task done at the start of the year, but if you assume mediocrity is the norm, as it is in most of the world, they likely don't have the J-20 flying with Chinese engines yet.
It said so in the text itself, that flying with domestic engine is first priority. I would say that's pretty important, too.