Originally Posted by
jsloan

Let's hope it doesn't come to that. In my case, it'd be the flight
from Singapore. Since it's a TAP flight number, EC.261 probably applies, but I'd rather not have to find out.

But I really don't expect it to get to the point where people are being denied boarding without notice.
iirc it's the OPERATING airline that is accountable for EC261. so, the long leg either way wouldnt count.
However, for eastbound flights it's the arrival time at SIN that counts (so if you have a long FRA transit, it can absorb any delays that doesnt eat into the FRA departure)