Kathmandu, January 27 More than 20 international and domestic scheduled flights at the Tribhuvan International Airport (TIA) were affected today morning owing to poor visibility due to bad weather. Flights to and from the airport were affected for three hours (6am to 9am) due to poor visibility at TIA triggered by thick fog in Kathmandu Valley, according to TIA officials. Airlines have their own visibility manual for take-off and landing of aircraft. Though visibility of 800 metres is taken as fair for outgoing international flights at the airport, visibility of above 1,600 metres is imperative for aircraft while landing. However, the lowest visibility at TIA today was measured at 100-200 metres at 6am while it gradually reached 1,600 metres at around 9am. In the case of domestic flights, a minimum visibility of 1,600 metres is necessary for both take-off and landing. “Scheduled flights resumed in a full-fledged manner after 9am,” informed Pratap Babu Tiwari, spokesperson for TIA, adding that the foggy weather has been affecting scheduled flights repeatedly. TIA officials informed that a number of domestic flights, especially those scheduled to mountain regions were postponed while a few international incoming flights were put on hold. Among others, a Qatar Airways incoming flight overshot the TIA runway today and was kept on hold for almost an hour following the bad weather at TIA. Currently, 29 airline companies, including three Nepali airlines have been conducting international flights from TIA — the sole international airport of the country. Similarly, 20 air service providers, including 10 helicopter operators have been conducting regular flights to various domestic destinations from TIA. Raj Kumar Chhetri, general manager of TIA, said that flight obstruction in the morning during winter season has become a normal phenomenon. “As visibility is directly related to the safety of the flight and passengers, flights cannot be operated without accurate visibility,” he said.