Center Controller and the Controller in Charger reported a general aviation aircraft encountered icing and temporarily lost control descending below the Minimum IFR Altitude.
Synopsis
Center Controller and the Controller in Charger reported a general aviation aircraft encountered icing and temporarily lost control descending below the Minimum IFR Altitude.
Narrative
Aircraft X was a ZZZ departure going west who came out of ZZZ Approach. On initial check in he said he wanted to go as high as possible to get over icing. I climbed him to 170. I got a report from an airliner who departed ZZZ1 southbound that he broke out of the cloud layer at FL190. I relayed the report to Aircraft X and clarified what it meant as he was confused by the term 'breaking out'. A few minutes later I asked if he was getting icing in that area. He said 'a little bit on his windshield; a small amount'. I filled out a PIREP with this information. Several minutes go by and he then told me he had rime ice on his windshield. I described the precipitation areas on my scope which were approximately 80 miles east of him and 50 miles southeast of him. and I noticed that his climb had stalled out at 120. I asked him if he was still climbing or if he wanted to stay at 120. He replied that he could see some blue sky and wanted to continue climbing. About 30 seconds later he declared 'in an uncontrolled descent'. I told him about the MIA in that area; 090. I observed he was in a right turn and asked if he was able to maintain any control; he said 'negative'. He came back a short time later and had control. I told him to maintain at or above 090. He responded he was out of control again. He was able to regain control and said he had icing on the wings. I suggest two nearby airports; he opted to go to ZZZ2. Over the course of the next few minutes I gave him an initial vector to ZZZ2; followed by another vector after he veered off course. I gave him the airport weather; elevation; runway length and the three instrument approaches. He eventually descended to 090; and then to 080. By this point he said the icing was starting to melt from his windshield and he had control of the airplane enough to start the RNAV approach to Runway XX. After he passed the initial approach fix he began descending to 075. I gave a low altitude alert and reminded him the MIA was 080 in that area. I checked to see that he had pitot and carburetor heat turned on and he did. By this point he said the ice was melting and the temperature outside was 35 F. The rest of the flight was pretty normal all things considered other than he stayed at 075 despite the minimum IAF altitude of 080. He was well above the highest point in the area and he was between layers at the time. He ended up landing with no other issues.There were several things looking back now that could have tipped me off to the danger he was in. The first being the extremely slow climb in icing conditions combined with a gradual reduction in his groundspeed. It was shortly after I told him about the stopped climb that he lost control. I do question whether I caused him to try a steeper climb which resulted in him stalling and losing control. I think also having him descend back to 090 which was a safe altitude to get back into warmer air could have been helpful; despite him wanting to climb above the layers of icing. Also I was reminded several times by management that he was below the MIA; a fact which I had told the pilot already. I was extremely hesitant to give any indication to the pilot that he needed to immediately climb back to 080 out of fear that he would stall and lose control again.
Second reporter narrative
I will be discussing the Controller in Charge (CIC) role I had and actions made. Before and during the incident I had sector split out due to icing reports. It was not busy but we had sufficient staffing to have it open. Sector XX solicited for pireps and received a trace icing previous to the incident. At around XA:45 I was sitting right next to the controller when he advised that he had a situation. I immediately told the supervisor in the adjacent area to get the OM so I could immediately start working on the incident. Within 2 or 3 minutes the OM and the area supervisor were in the area to help. I plugged in with a handset so I could hear the situation and not have to have everything relayed to me. I made sure the sector had a D side staffed to help. After the pilot gained control of the aircraft again I went over to sector XY empty scope and started to look at the weather at all the surrounding airports to see if anywhere was reporting VFR. They were all similar with IFR reports. The aircraft was closest to ZZZ2 so we determined that was his best option. Unfortunately; the aircraft could not maintain altitude and was flying under the MIA. I listened to a Low Altitude Alert to the aircraft. After the aircraft decided to go to ZZZ2 I relayed that information to the OM so they could have the vehicles ready at the airport. I then coordinated with sector XZ (sector above XX) to have an aircraft turn the lights on at the ZZZ2 airport for the pilot. We were constantly looking at the terrain chart and although the pilot was at 7;600 ft (MIA 8;000) the actual terrain underneath him was 5;600. The terrain was not an immediate threat and making sure the pilot was keeping the aircraft under control and navigating the correct course seemed most important. I made sure the D side pulled up the NOTAMs for ZZZ2 to make sure nothing was going to restrict his approach. Throughout the process we had to 2 pilots come help from another area to help with any additional information that would be helpful. I had sector XZ put an aircraft on the Unicom frequency to help relay any information from Aircraft X. We eventually got a 'safe on the runway' report from the relay aircraft. The radar controller did a great job helping the pilot get on the ground safely. The OM kept asking us to keep issuing Low Altitude Alert warnings to the aircraft. The pilot was well aware of his situation and telling an iced up pilot on a procedure turn inbound to the airport a Low Alt Alert was not a helpful idea. We knew the terrain and knew the pilot had icing and was aware he was under the MIA. The aircraft was already slowed to 76 kts. If we told him another time 'Low Alt Alert suggest you climb immediately' during this critical phase of flight he might have pulled back and stalled the aircraft.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.