The season is short for trekking and climbing, it doesn't last all year. The trecking season is generally October/November and February/March to catch the best weather and avoid the extreme cold and monsoon. There are many aircraft accidents in Nepal, the only Royal Nepalese Airlines 'Pilatus Porter' which got myself and my wife out of Shyangboche, crashed during the same run two weeks later, killing the pilot. Whilst we were flying out the owner of Yeti Airways, the company that flew us to Lukla, was killed along with the helicopter pilot, when it crashed, whilst on a rescue mission to collect a Belgian trekker suffering altitude sickness. he died too.
It's a fantastic place all the same, you just have to do it - you takes your chance.