Hypothetical or unrealistic?
CF6
I think it's great that people can post questions and discuss the answers. I'm always ready to learn which is why I read this thread so nothing wrong with that.
However, your question was, in my humble opinion, not so much hypothetical but unrealistic. You may disagree but I'll explain my reasoning.
On a manually flown approach my company always recommends disengaging the autothrust. I don't think it's prohibited as such but the pitch power couple makes it clumsy so no autopilot then we use manual thrust. In fact with the CF6 and metric weights it's a easy to remember the power setting as it's 6 plus the middle digit of the weight eg 240 tonnes use 64%. Add about 8% so 72% if one engine inop. Useful info every 6 months or so!
I'd never thought about it but yes I suppose if, contrary to the recommended technique, one left the autothrust (A/T) engaged then perhaps it will still retard the thrust in "idle" mode at about 25 ft radalt. Of course that's one of the cues one looks for in an autoland along with "flare".
I'd never heard of FLCH trap until the Asiana crash and as someone else mentioned it might be an issue on the 777 and 748 but not the 744 although I'm happy to be corrected but it doesn't ring any bells and I've read the FCOMs a few times.
If there is a trap of sorts then it's the fact that TOGA as a mode is not available after a prescribed time and height - 5 radalt and 2 seconds? While I remembered that in the context of an autoland it surprised a colleague who rejected an approach very late, the classic "floater", then realised hitting TOGA wouldn't work. No problem once he realised of course back to basics. There but for the grace of God!
Hope that helps.
BBK