On 16 February 2014, Nepal Airlines Flight 183, a de Havilland Canada DHC-6 Twin Otter flying from Pokhara to Jumla, crashed into a hillside at Dhikura in Arghakhanchi district. The crew had been trying to divert to Bhairahawa because of bad weather. All 15 passengers and 3 crew were killed.
In short: The crash was attributed to controlled flight into terrain in cloud. It came weeks after the EU listed all Nepali airlines and strengthened calls for better oversight of mountain flying.
Mountain flying in Nepal
Twin Otters serve short, remote airstrips such as Jumla, Simikot and Jomsom. Weather changes fast and many routes lack radar coverage. See EU air safety list and Tara Air crash, 2016.