A Case Study on Assessing Cumulonimbus Induced Flight Vulnerabilities Over the Nepalese Himalayan Terrain

With a boom in the tourist industry both in India and adjoining Nepal, middle-class tourists from the Indian subcontinent have started routinely flying over the Himalayan terrain over the last decade. This influx of tourists stretches its aviation sector, in a country with some of the most vulnerable airports. The Himalayan terrain plays a key role in shaping weather systems over the region which has witnessed several aircraft crashes. Tourists in Nepal routinely fly 19-seater aircrafts such as the Beechcraft 1900D for a joy ride over the Himalayan range and are particularly vulnerable. This paper assesses the risks and vulnerabilities associated with such short duration flights starting from Kathmandu and covering parts of the Himalayan region. The region experiences deep cumulonimbus clouds which form over a period of a few days and are ubiquitous during the monsoon season (June to September). The vertical extent of such clouds ranges from 2 km upwards to up to the tropopause. This paper first assesses cumulonimbus mediated hazards along flight routes with thunderstorm activity and then details a critique on the hazard tied down to secondary effects i.e. deposition of supercooled droplets on a Beechcraft 1900D. In particular, the paper explores the role of cumulonimbus induced icing on the aircraft surfaces which can severely affect tourist flights over this part of the developing world.