There has been a lot of airframe stiffening and software update,going on since the first crash, in November 2011.
At the time there were unknown weaknesses in the wing structure and the flight computer allowed the aircraft to go beyond its structural capability.
Combination of both caused the wings to flex so much that the aircraft lost the necessary lift.
On this occasion it was too close to the hills and could not recover.
Payload capability is higher in block 3 , but i am not sure how high.
Likewise there was an issue with the air to air missiles provided by the Chinese.
I used to know a guy who was on the Radar network of PAF He told me that Block 2 was tested for locking on aircraft size targets at 70 km range and done so multiple times. But PAF had reliability issues with the missiles. The algorithm which maneuvered the missile to within close proximity of enemy aircraft was not reliable.
All those issues are now settled.
Anyway here are some pics of 2011 crash due to wings failure.
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