Owning to its demanding geographical location and climatic variation, the domestic flights in Nepal are mostly prone to flight delays and cancellation. Due to adverse weather conditions such as, heavy rain, thick fog, strong winds, etc. may lead the flight delay or cancel. Also, the topography of Nepal is difficult; therefore it is safe not to take off the flight in those adverse weather conditions.
So, autumn season (October -November) and spring season (March-April-May) is the most preferred trekking season when the weather is dry, clear and stable. At this time of year, flight delays and cancel is rare. For other seasons, weather cannot be guaranteed. Monsoon season (June- August-September) is highly prone to flight delay and cancel. The strong winds, rain and patchy clouds make the view unclear. Also, in winter season, flights may get cancelled due to thick fog.
Therefore, if you are travelling to Nepal, it is recommended to have one or two days spare in case your flight gets cancelled and you are in short of scheduled time. In other cases, road transportation can be an option. However, in case of flight to Lukla, you may have to change your entire schedule.
NOTE: Travel Insurance is highly recommended. In case of flight delay or cancel in the mountain airstrip, and maybe you are unable to catch your flight back to Kathmandu and to your home. In that case, Waiba Adventure trek can arrange charter or sharing helicopter at your service. However, the cost should be borne by members.