In which temperature range is the most rapid accumulation of clear ice on an aircraft likely to occur in flight?

The most rapid accumulation of clear ice on an aircraft during flight typically occurs within the temperature range of 0 degrees Celsius to -15 degrees Celsius. This is primarily because the conditions in this temperature range enable large supercooled water droplets to exist, which are capable of freezing upon contact with the aircraft's surfaces.

At temperatures just above freezing (0 degrees Celsius), water droplets can remain in a supercooled state, meaning they have not yet frozen despite being below freezing temperatures. When these droplets collide with the aircraft, they can freeze rapidly, forming clear ice, which is dense and heavy.

As temperatures drop below 0 degrees Celsius, the size of the supercooled droplets tends to decrease, leading to more rime ice formation rather than clear ice. Additionally, in the colder ranges, particularly from -15 degrees Celsius and below, conditions become less conducive for large droplet accumulation, leading to slower rates of icing.

Therefore, the conditions between 0 degrees Celsius and -15 degrees Celsius are optimal for rapid clear ice formation due to the presence of larger supercooled droplets and the dynamics of freezing upon contact with the aircraft's surfaces.