The 3-Kelvin-spread rule, an aviation rule of thumb for winter operations, can enhance pilots’ sense of the actual landing risk level by calling attention to the likelihood that aircraft braking performance will not meet pre-landing calculations. The rule takes advantage of information readily available from aviation routine weather reports (METARs), and its potential value has been recognized in the recent report of an investigation of winter operations1 by the Accident Investigation Board Norway (AIBN; ASW, 10/08, p. 14 and 11/10, p. 30). Nevertheless, its ease of adoption comes at the expense of absolute validity.
The rule emerged from several years of scientific research and analysis in Norway, including my contributions in the report’s Appendi…
