B737 flight crew reported incomplete ground deicing process and procedure resulting in APU shutdown and contamination remaining on the aircraft after the deice process due to fluid failure. The aircraft returned to the gate to have the contamination removed.
Synopsis
B737 flight crew reported incomplete ground deicing process and procedure resulting in APU shutdown and contamination remaining on the aircraft after the deice process due to fluid failure. The aircraft returned to the gate to have the contamination removed.
Narrative
We arrived to the airplane in ZZZ that had sat overnight and had ~9 inches of snow on it. The aircraft was pushed back after some delay and we communicated the need for Type I full body and Type IV wings and tail. This process took over an hour due to the large amount of snow on the aircraft. During the Type I application the FO (First Officer) and I observed multiple areas of snow still remaining on the aircraft; including the nose and both winglets. We had to communicate this to the ground crew and get them to re-treat these areas and explicitly ask them to clear the remaining snow. This was not new snow that had fallen but remnants from the night before (the nose was mixed with Type I and the winglets did not appear to have been treated). During the process the APU dropped off the transfer busses; presumably due to fluid entering the inlet and causing an over-temp. We received the application information from the ground crew and proceeded to start the engines. We taxied with the flaps up and; due to the short holdover times; contamination on the nose (inconclusive nose check) and concerns with the deicing process; elected to complete a wing check with ~13m remaining on our holdover time. The FO completed the wing check and when she returned said that the fluid had failed in multiple places and she was concerned with large patches of snow still on the aircraft; particularly on and around the engines. We returned to the gate to offer egress and discuss the icing issues. I conducted a visual inspection and found failed Type IV fluid; as expected; but a considerable amount of snow on both engines and pylons. There was considerable frozen accumulation forward of the engine ingestion warnings. In some places there was Type IV applied on top of the snow. I also found ice inside both engines that had solidified after shutdown and would require maintenance to come remove before we could attempt another start.We deplaned while I called Dispatch and the chief pilot to advise of the situation. It took a couple hours to get the ice removed from the engines at which point we were able to depart and deice uneventfully.The Type IV may have failed because of the poor conditions but; given the significant amount of snow I found still adhering to the aircraft; I'm under the impression that the aircraft was never properly deiced in the first place and the remaining contaminants contributed to the fluid failing. The contaminants that we found remaining were unacceptable.
Second reporter narrative
Our flight # ZZZ-ZZZ1 pushed back 17min late from Gate XX due to deep snow impeding the tug in the gate area. We asked for deice/anti-ice; Type 1 Full body; Type 4 wings and tail. There was a large amount of snow on the airplane from the overnight and current snowfall (RVR as low as 2800 during this time). The deicing took a long time to remove the snow and the Captain and I noticed snow accumulating on the nose by our wiper blades. We also noticed patches of snow on the inside leading edge of our upper winglets. The truck started Type 4 fluid application so we talked to operations on the interphone and told them the nose and winglet needed Type 1 again. In the middle of this deice/anti-ice application; the transfer buses disconnected from the APU. The APU didn't shut down; so we reconnected the buses and turned the yaw damper; the autothrottles; and the rejected takeoff auto brakes back on and talked to Maintenance Control to get clearance to continue. Maintenance Control gave the all clear - saying it was an high temp indication on the APU controller; presumably caused by ingested fluid - and by this time the trucks were finished deice/anti-icing.An operations agent connected to our interphone via headset relayed all the Type 1 and 4 data (for 3 trucks) and confirmed aircraft clear of snow and trucks clear of aircraft and that we were cleared to start engines. Our holdover time showed 30min left before type 4 expiration as we taxied out to Runway XX.Holding short of the runway; I performed a wing check both because the nose check showed precipitation sticking to the nose; and because we had lost confidence in the fluid application since the Iceman had missed snow on the wingtips. During the wing check; I saw thick snow on top of both engine cowlings that had never been deiced with Type 1 and instead had small amounts of Type 4 over the top of the layer of snow. The Type 4 fluid had also started to visibly fail and become opaque on the trailing edge of both wings. We coordinated a return to gate to offer egress as well as get deiced and anti-iced properly.My Captain did a postflight walk around and found multiple area of failed fluid on the wings and thick snow over cowlings from the overnight snowstorm. FOM outlines the clean aircraft concept includes no precipitation forward of ingestion warnings; and we can only conclude that these areas of thick old snow were never deiced with Type 1. My Captain also found new snow and ice accumulating on the engine spinners and inside the inlets. We called Maintenance and deplaned. It took a couple hours for Maintenance to remove the ice in the engine inlets. We boarded the passengers again; deiced; anti-iced; performed a wing check short of Runway XX again and this time the airplane was clear of contamination and the type 4 fluid was still glossy and effective. We departed without incident.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.