That's what the Communist Party-controlled news media says, but can we believe it? I'm not so sure.
It's actually quite a reasonable claim, considering all the WS-10s in mass service are aboard Flankers, which are twin engined aircraft... meaning such an aircraft would usually need both engines to fail to actually allow it to crash.
And yet, we haven't seen any J-20 test planes using WS-10 engines. Why is that?
Probably because during the J-20's early test phase the Al-31s were judged to be more reliable and a better known quantity than WS-10 (this was five years ago, remember) and so they went with Al-31s instead.
Now in 2016, it is likely that the air force's (or CAC's) assessment and confidence of WS-10's reliability and performance is far greater than in 2011, but for J-20s development it makes no reason to switch to a WS-10 variant because WS-10 probably does not offer an overwhelming advantage to the Al-31s in many important domains such as thrust or reliability or MTBO. If they did switch to WS-10s for J-20s, it would introduce additional costs and time to J-20's development and testing phase, but the lack of significant advantages in performance compared to the Al-31s currently being used, probably makes those costs not worthwhile.
Therefore, it's likely that we won't see WS-10s on J-20 at all to replace Al-31s because even if WS-10s are better than Al-31s, they probably are not that much better, and it's more sensible to wait for WS-15s instead, where the additional cost and time for integrating and testing the engines will produce a much more significant increase in capability.
On the other hand, if the source of Al-31s for J-20 eventually dries up for some reason, then they will probably have to use WS-10s and they will have to contend with the costs and delays in integrating a similar engine to replace the Al-31s in the first place.
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On a tangent, I've noticed over the years of talking about engine development, that people tend to over simplify the relationship between engine capability/performance and whether it is adopted or not.
That is to say, most people believe that if engine X is adopted over engine Y for a particular aircraft, then it must mean engine X is therefore inherently and significantly superior to engine Y -- but there are a massive number of confounding factors which are arguably as important if not more important than sheer performance of engines.
These factors can include: cost to performance ratios of both engines; the cost and time of integrating a new engine vs another; the production rate (and thus availability) of one engine versus another and whether the production rate of one engine type is enough to fulfill airframe requirements; the familiarity of an air force for one engine vs another; and whether the existing logistics infrastructure of an air force is already better suited to one particular engine versus another, etc.
