In Feb. 2000, when I flew UA845 SFO-TPE in C, my PTV wasn't working (if this counts as a mechanical problem). My mom switched with me because she doesn't care about IFE.
When we deplaned in TPE, a FA gave us a coupon for 5000 bonus miles.
Btw, read the LHR-BOS part of Tfung's awesome trip report. Everyone had to deplane because of a broken door seal, but they got a free meal at the airport restaurants.
www.flyertalk.com/forum/Forum81/HTML/002779.html
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9V-SMU
The 1000th 747
Currently operated by Singapore Airlines