Hei
Theres an A340 that internet has never worked on at all, have been on that aircraft only once.
The service sometimes disappear around the beginning of Greenland flying CPH-ORD, but it usually comes back after an hour or so.
On CPH/ARN-EWR it has worked 100% for me.
Have used the service 11 times total, it has worked 100% 7 times.
I think thats pretty good.