Date: 201701
Location: EWR.Airport, NJ
Flight conditions: IMC
Weather elements / visibility: Rain
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Taxi
ATC / advisory: Ground EWR
Reporter organization: Air Carrier
Reporter function: Dispatcher
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Became Reoriented
Contributing factors: Company Policy; Human Factors; Weather
Primary problem: Ambiguous

Narrative: Flight pushed at EWR and after push ATIS and METAR changed to indicate -pl which would leave an allowance time of :10. Captain called and said no pellets just rain. While talking with captain ATIS and METAR amended to delete pellets and show just -RA. Captain questioned whether as an onsite observer he could say no pellets just rain. Called Chief and he stated that if Company X was not reporting pellets then we were legal to go. Captain concurred and flight took off. Captain ACARS later to say the following:FYI WE WILL DO A REPORTABOUT THE RAPL WX AT EWR..SEEMS LIKE A LOT OF.CONFLICTING GUIDANCEBETWEEN THE FOM+ THE HOT ACARS LWE INFO..IT WOULD BE GOOD TO SEE WHAT IS THE.MASTER WX SOURCE..ATIS..EYEBALLS..OR LWE..Our Weather Service reported nothing but rain during the entire event.


Second narrative: Upon arrival at the aircraft ATIS was reporting RAPL BR (temp 03) while the EWR Liquid Water Equivalent (LWE) system was calling RA only. Captain called dispatch and was told that ATIS is controlling. While coordinating a game plan a new ATIS was released that reported the precipitation as RA BR so we pushed and began our taxi. During the taxi a Special ATIS was released again calling the precipitation RAPL BR. We stopped our taxi and I pulled up another Hold Over Time (HOT) message (which reported only RA and no holdover times) while the captain called dispatch again. While on the phone with the chief dispatcher; ground called us and told us that company was informing the tower that we were ok to proceed because the HOT message was controlling. Shortly thereafter the chief dispatcher told the captain that the message was controlling if; at pilots discretion; we only saw rain and no freezing precipitation. We elected to continue as the LWE messages over the course of an hour had consistently shown only RA with no holdover times. We felt confident in the report as we could only see rain and the visibility was 4 SM.The issue at hand is confusion over what the controlling weather agency is. Do the HOT codes utilizing LWE technology take precedence over reported ATIS or does ATIS override the HOT messages and force us into the HOT app? The FOM and pilot bulletins regarding the matter are vague and seem somewhat contradictory. The Bulletin makes it seem like ACARS HOT messages are controlling. Yet the FOM says takeoff is prohibited with certain types of precipitation. What do we do when the HOT and the ATIS disagree on the type of precipitation? Adding to the confusion our hold over tables have holdover times for the prohibited precipitation types.


Synopsis: B737 flight crew and Dispatcher reported confusion concerning the legalities of a departure with -pl on the ATIS and only RA on the Hold Over Time app.