The decline into death of the British aviation industry and contemporary slide of Britain from a unique world power back into the pack with all of the other big-medium powers. There is nothing structural, these were human decisions that could have gone the other way.
Even by the standards of AH.com with its adoration of the British Empire, saying that the fall of the British Empire was ASB is probably a record.
Britain was not a unique world power. It was a great power with large colonial holdings, in a world with many great powers with colonial holdings. Any differences between it and its contemporary great powers were that of degree, not substance. One could argue that it was the closest the 19th century got to a superpower, but Britain never towered over its contemporary great powers anywhere near the degree the US and USSR towered above their contemporaries post-1945.
Britain's high-status was dependent on it having and maintaining said Empire. This empire, by virtue of being an empire, was largely comprised of non-British people. These non-British people, by virtue of being human, tended to resent not ruling themselves and being ruled by foreigners. If the British were to treat the non-British as true equals, the British Empire would promptly cease to exist as the
British Empire and would turn into the
Indian Empire, because that's where the demographic weight lay. The British naturally didn't care for that so they didn't do it, while the Indians (and Nigerians and Kenyans and Egyptians and so on) didn't like being second-class citizens in their own country.
Given the demographic discrepancy between the imperial (British) people and subaltern (everyone else) peoples and that natural human strain, the fall of the British Empire was inevitable, just like every other empire. It's the exact opposite of ASB. The area of variation is restricted to the details and timing of said fall.