Oh dear. WordPress.com appears to have started doing annoying ‘second guessing’ on keyword search in a free blog.
Searched for aviation. Wasted time with results that only have airport or aircraft in them… and no sign of the aviation keyword required.
Searching for “aviation” makes no difference. And it’s not distinguishing between capital-A Aviation and aviation either.
The best option (for those with huge blogs, rather than those who struggle to produce six posts a year) now seems to be to download your .XML archive, and then have that in a folder indexed by desktop search software (DocFetcher etc). The problem there is that the post you’re looking for is likely a recent one, and may not be on the older local archive.