Originally Posted by
safetypee
Runway reports are determined and reported by ATC; it is assumed that this based on the TALPA matrix.
Frost is considered wet, but rime is not stated; this problem involves judgement of the difference between frost and rime; how ATC assess and report rime.
Many situations in aviation consider rime to be associated with ice. Technically rime should not be reported, if it is then question ATC; beware of other pilots interpretation.
Thus, if frost use wet performance, but there is some uncertainty reduce the reported condition by one category and check the safety margin, and a further reduction if the OAT is +/- 3C.
If rime = ice, then no go.
If still not clear then Air Safety Report to operator, regulator, and manufacturer.
Maybe I should be careful to say Boeing as we use a third party performance tool.
Contamination can be of two types: The one that creates resistance: Snow, wet snow, dry snow, standing water, slush. No resistance, Dry ice, wet ice, rime, frost, wet.
If any type of ice is a no go for you, then I understand why rime and frost would be classified as wet.
We can take off on dry ice and use the required performance calculations for this. Rime and frost (reported by ATC) is classified as dry ice.