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; AS W, 10/08, p. 14 and 11/10, p. 30). Nevertheless, its ease of adoption comes at the expense of absolute validity.
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机译：3开尔文散布法则是冬季操作的航空经验法则，它可以通过引起人们注意飞机制动性能无法满足着陆前计算的可能性，来增强飞行员对实际着陆风险水平的认识。该规则充分利用了航空常规天气报告（METAR）所提供的信息，并且挪威事故调查委员会（AIBN; AS W，10/08，第14和11/10页，第30页）。但是，其易于采用是以绝对有效性为代价的。
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