Mine was the flight from Bangkok to Tokyo that took three days to complete.
I was due to fly out of Bangkok on the now, thankfully, defunct Air Siam.
After a couple of hours delay we took off but about two hours into the flight we suddenly returned to Bangkok with engine trouble. We disembarked and sat around for a few hours before the ' staff ' bundled us onto a bus and put us in a hotel for the night.
The next morning we took off again but after only fifteen minutes further engine trouble caused us to return to Bangok for a second time. After another lenghthy wait we got underway again and headed for our first stop- Hong Kong.
About an hour before reaching HK the pilot informed us that a typhoon had closed HK airport and we were rerouted to Taipei. We got off and spent several hours in the transit lounge . The all clear came towards evening and we finally landed in a very blustery HK.
Narita airport (Toyko) was now closed for the night so we stayed in a HK hotel. The next morning we finally took off and managed to reach Narita in the afternoon without any further problems. Total time, three days.