UA890 Dumps Fuel
I happened to catch most of the drama on the in-flight audio system, which had a channel with all of the cockpit and cabin-to-cockpit audio. About 100km out of Narita, the head stewardess called to the cockpit to report that a wall was very warm, there was an electrical smell and wind noises. The pilot sent down the first officer and about 5 minutes later, I heard the pilot declare an emergency to the Narita tower. I had what you might describe as a sinking feeling. There wasn't an announcement at that point, but about 15 minutes later, the first officer came on and said there was a mechanical problem that was of enough concern to go back, all in a very calm voice. I noticed that most of the cabin crew made themselves visible and carried on gregariously, laughing and telling each other stories and I could only imagine that this was meant to keep people calm and happy. I, on the other hand, am enough of an aviation buff that I've read a few books containing transcripts of cockpit voice recordings that preceeded accidents. (This isn't a morbid fascination, but a result of my masters studies at the University of Washington where I was involved in work on human factors issues in airplanes — how to make things that could go wrong, not go wrong, basically — and most of this work was funded by Boeing.) On the one hand, I was exceptionally relieved that the pilot immediately declared an emergency because many "emergencies" become fatal accidents when pilots underestimate what may be wrong or because they feel some sense of pride and want to deal with the problem without bothering anyone else — these are part of that awful category of "pilot errors"), on the other hand, a very warm wall immediately sounded like overheated electrical conduits or, worse - fire. About 10 minutes later the captain came on the PA told us what he knew, and he didn't seem to try and occlude any facts. They thought it was a problem with a heating duct after they had turned the heat off in that part of the plane and the noise died down and the warm wall wasn't as warm any more. But, we were going to go back to Narita, which was fine by me. We had to dump fuel (probably about 11 or 12 hours worth, I'd guess) for about 15 minutes over the Pacific, doing lazy-S's as we snaked back toward Tokyo.
This AP Feed says there was smoke in the cabin. From where I was, about 25 rows behind, there was none.