For the second time in recent years, a plane headed for Lukla crashed in the mountains, this time killing 3 crew members and 11 passengers, 6 of of them being foreign tourists. More on the previous disaster which happend in 2008 can be read here: Airplane crash on Everest route kills 18. Lukla is a popular jump-off point for the Everest trek and is one of the busiest airports in Nepal.
The pilot apparently reported generator failure en route to Lukla and decided to return, but the backup generator also later failed. Without cockpit avionics the plane would be flying blind in rugged terrain and heavy rain. The cause of the crash would seem to be a combindation of technical failure and bad weather.