Currently there're two ways to get to Lhasa from Kathmandu.
Taking a flight to Lhasa from Kathmandu. There is at least 1 direct flight from Kathmandu to Lhasa every day (during peak tourist season, there're 2 flights). It takes around two hours to arrive in Lhasa, which is the quickest way to reach Tibet from Nepal. However, the flight is always delayed due to the unstable weather condition. Sometimes, it will be even canceled and put off to the next day, which could disrupt your original tour plan indeed. So, travelers should have known this possibility in advance.
