Date: 201412
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Icing; 4
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch; Taxi
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Training / Qualification
Second reporter function: Captain
Anomaly: Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented

Narrative: Prior to pushback from the gate and subsequent engine start; the weather was overcast with good visibility.  After pushback; rain began to fall and a new ATIS was forthcoming.  We obtained the new ATIS prior to taxi and discussed the -FZRA indicated with the new weather broadcast.  The aircraft had been deiced prior to Crew arrival with Type 1 deice fluid and the deice form was included with the Dispatch Release. We made a visual check of the aircraft on taxi out and noted no ice present.  Ground Control contacted us while taxiing and said that an aircraft in the deice pad (another carrier) was concerned that he had ice on his aircraft and that he noted we were not going to deice.  We checked our wings and informed Ground Control that we had been deiced at the gate and that our aircraft was free of contamination.  We proceeded to receive our takeoff clearance and departed without incident.  During the cruise climb portion of the flight; the Captain confessed that he was having reservations about the decision we had made to takeoff without anti-ice.  We pulled the winter ops laminated cards and reviewed them and discussed the information contained on them.  We agreed that we did in fact error in our judgment.  We should have taxied to the deice pad and been deiced and anti-iced with Type 1 followed by Type IV fluid.  Although I was uncomfortable with our initial decision and had reservations of my own at the time; I failed to convey that to the Captain and I believed that we made a safe decision.  The first indication of -FZRA on the ATIS should have sent us to the pad for deice.  The indication from another aircraft of ice should have sent us to the deice pad.  We should have reviewed the laminated cards initially and that would have left us with no doubt given the circumstances.  This was my first real-word Company winter ops situation and we should have taken more time to study what we were dealing with.  I will better prepare by reviewing FOM again and the laminated cockpit reference cards.


Second narrative: Our aircraft had been deiced with Type 1 fluid prior to Crew arrival and the Agent gave us the de ice form. When we pushed; there was no precipitation; and the ATIS had no visibility qualifiers either. Just after push and both engines started; precipitation started falling; and a new ATIS came out that had -FZRA. The First Officer (FO) and I talked about it; checked the aircraft; and noted that nothing was adhering; and continued to Runway. Ground Control called us as we were approaching the runway and told us an aircraft in de ice another carrier called and was concerned because he had icicles on his aircraft and noted that we had not de iced. We checked our wings and told Ground Control that we had been deiced at the gate and our critical flight control surfaces were free and clear of all contaminates. We took off uneventfully. I started second-guessing my actions at cruise altitude and looked more closely at the deice cards. As I looked at the cards; clearly; I should have deiced. The First Officer and I read the cards and we both agreed. Since we went from no precipitation to -FZRA; we should have taxied to a remote deice pad and done a two-step de icing. The holdover time can't be extended with a cabin check. I got confused on the ground; thinking that with our de icing prior to arrival and the fact that our control surfaces were free and clear; we were good to go. Not true. I should have stopped and read the card. This being my first deicing event this year; I was not prepared for this possibility; and was not even thinking about deicing while observing the overall weather prior to pushback. It was just cloudy and overcast.


Synopsis: B737-700 flight crew reports departing with light freezing rain falling; without being anti-iced with type IV fluid. A study of the de ice sheet indicates they should have deiced with type I and anti-iced with type IV.