Following lengthy ground delays in blowing snow the A319 flight crew returned to the gate to be de-iced a second time. Visual inspection of the wing leading edge discovered ice the length of both wings despite a time interval of less than the calculated holdover time.

Narrative

Winter storm conditions were in effect at ZZZ that at push from the gate was moderate rain and ice pellets. During taxi; it changed over to blowing moderate wet snow; lengthy delays for deicing; temperature +2 degrees C; and a gate return was forced once taxi fuel burnout became excessive. After returning to the gate; I (the Jumpseater) stepped out onto the jet bridge to inspect the wing for ice/snow to see how well we did 1 hour after a 2 step deicing/anti-icing and still within the holdover time. I found the top of the wing clean; but the entire length of the leading edge was impacted with snow. The Captain had followed procedures for winter operations; kept alert with changing weather conditions; and was very aware of holdover times and an effectiveness of Type 4 anti-icing fluid properties. Since snowfall had tapered off somewhat; he was OK with going longer into the holdover range. Yet in spite of this; I found the leading edge was contaminated upon returning to the gate. I believe the contaminated leading edge is the result of an industry misconception about the re-accumulation of contaminants on a clean wing. Most of the wing surface is horizontal and had a Type 4 deicing fluid lying on top of it. The leading edge surfaces having been set for takeoff; sit in a near vertical position so it readily allows for gravity runoff of fluids; leaving the leading edge unprotected but still within the holdover range for a fluid which is missing from this portion of the wing. In spite of their best efforts; situational awareness; and strict adherence to company procedures for winter operations; they believe they were good to go for takeoff. A visual inspection of the wing just prior to takeoff would have easily spotted the contaminated leading edge; but not required according to procedure.