Narrative:

There is confusion amongst pilots and dispatchers about the proper use of type iv fluid holdover tables when mixed types of precipitation are present. Note 2 of the type iv holdover table states: 'use light freezing rain holdover times in conditions of very light or light snow mixed with light rain.' there are no other references to mixtures of other types of precipitation; which leads one to believe that other mixtures of differing precipitation types are not authorized; similar to the note on the 'ice pellet and small hail chart' which states: 'if a precipitation type other than those listed in figure 15.17 FAA ice pellet and small hail allowance times for sae type iv fluids is reported; takeoff is not authorized.'in our case; ATIS in pit was reporting -fzrasn. In consulting with the dispatcher; the chief pilot on call and another captain; we determined that our existing mixture of light freezing rain and snow in pit was not covered by note 2 of the type iv fluid holdover table and that we could therefore not takeoff (the note refers to a mixture of light snow and light rain; and we had light snow and freezing rain). All were in agreement with this assessment.at some point a pilot from the training center got involved and told everyone we could go after all. I do not know who he was; but he convinced the dispatchers and the chief pilot on call that his assessment was correct; so we went with it. We used the most restrictive holdover time after being sprayed with type iv. I do not know if we handled this incident correctly.if this incident was handled correctly; the type iv tables need to have another note added that tells us what to do for other mixed precipitation such as -fzrasn or -fzdrsn. If this incident was not handled correctly; the type 4 table needs to have a statement similar to the ice pellet/hail table stating that takeoff is not authorized with the precipitation mixtures other than listed or noted.

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Original NASA ASRS Text

Title: Air carrier Captain reported confusion regarding Type IV fluid holdover times when mixed types of precipitation are present.

Narrative: There is confusion amongst Pilots and Dispatchers about the proper use of Type IV fluid holdover tables when mixed types of precipitation are present. Note 2 of the Type IV holdover table states: 'Use light freezing rain holdover times in conditions of very light or light snow mixed with light rain.' There are no other references to mixtures of other types of precipitation; which leads one to believe that other mixtures of differing precipitation types are not authorized; similar to the note on the 'Ice pellet and small hail chart' which states: 'If a precipitation type other than those listed in Figure 15.17 FAA Ice Pellet and Small Hail Allowance Times for SAE Type IV Fluids is reported; takeoff is not authorized.'In our case; ATIS in PIT was reporting -FZRASN. In consulting with the Dispatcher; the Chief Pilot on Call and another Captain; we determined that our existing mixture of light freezing rain and snow in PIT was not covered by note 2 of the Type IV fluid holdover table and that we could therefore not takeoff (The note refers to a mixture of light snow and light rain; and we had light snow and freezing rain). All were in agreement with this assessment.At some point a Pilot from the Training Center got involved and told everyone we could go after all. I do not know who he was; but he convinced the Dispatchers and the Chief Pilot on Call that his assessment was correct; so we went with it. We used the most restrictive holdover time after being sprayed with Type IV. I do not know if we handled this incident correctly.If this incident was handled correctly; the Type IV tables need to have another note added that tells us what to do for other mixed precipitation such as -FZRASN or -FZDRSN. If this incident was not handled correctly; the Type 4 table needs to have a statement similar to the ice pellet/hail table stating that takeoff is not authorized with the precipitation mixtures other than listed or noted.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.