I read somewhere that 9/11/01 was the first time 3 of the 4 planes involved in the 9/11 incident had flown in 9 months. Does anyone know anything about this?

I've read something similar but was never able to confirm it and don't recall where it was. I was curious as to how this would correlate with the data from the FDR.

Hi, this is my first post here.
Like you and Kiask I've read things about the histories of the planes, but can't remember exactly where. I've seen it claimed that none of the planes were due to fly that day, and that some of them had been leased out to some defence contractor to take part in previous instances of the Global Guardian exercise.
Most of them were still listed as being in service for years afterwards too, apparently.
Then there's the pilot who claimed that he found himself parking up next to Flight 93 some months after 9.11
As for the FDR data :- somebody living near the Pentagon claimed that two weeks before 9.11 a large jet flew low over his house heading towards the Pentagon in the middle of the night. Perhaps that was the plane from which the FDR was taken to be passed off as Flight 77's.
So there seem to be quite a few claims about the planes' histories, and the 9 month claim is new to me. Worth looking for again - the sources must still be out there somewhee .

Aidan Monaghan was working on this issue. I did a quick search to find his orginal article, but here is a blog entry he made as an update. Hope this helps.

http://www.911blogger.com/node/20456

I'll try emailing Aidan as well and notify him of this thread.