I think the issue here is in the certified world there is significant testing on these systems even when FIKI isn’t the goal. With E-ABs, even RVs, there’s enough variation within like models to raise doubt that a given system will perform exactly as the aircraft used in development. For example without testing how do you know for sure that your system melts ice but doesn’t allow water to flow back and refreeze beyond the systems coverage? If I’m flying a Cirrus SR-22 with FIKI certification I have no doubts. But an RV-10 with a builder installed system— not so sure….
I found this ASRS report on RV-10 icing and thought it was worth including in this discussion.
Synopsis
Single Pilot reported flying into icing conditions and the control surfaces freezing.
Narrative: 1
I was in cruise on IFR flight plane in VMC talking with Center at 15000 ft. The cloud tops were rising and I requested a climb to 17000 ft. to avoid the tops. The sun had set and light was fading. I initiated a slow climb and monitored my wing leading edges with a flashlight as I flew in and out of a few thin tops. I observed a trace, to light amount of mixed ice. Center advised a jet reporting tops at FL190 and asked if I wanted FL190. I replied I could try but did not think I'd make it due to aircraft performance. Upon reaching 17000 ft., the aircraft did not level off while the autopilot was engaged. I had been monitoring my AoA [Angle of Attack], 200-300 FPM climb resulted in AoA active, but well above donut, and noticed the aircraft remaining in a 200 FPM climb. I disconnected the autopilot (AP) as the AP commanded full nose down trim. I commanded a nose down control input via the control stick and could not move the stick in a fore or aft motion. I still had roll control but had no pitch control. I applied considerable force – I was afraid of pushing too hard and breaking something, not knowing what had frozen the controls – and could not induce a nose down attitude. I asked for an immediate descent with Center and was granted an altitude of 15000 ft. ADSB weather indicated a heavy to extreme precipitation below my position with bases of 6 - 8000 ft. I commanded full up elevator trim and confirmed movement via trim indication and a reduction in climb rate. I visually confirmed the elevators were stuck in an approximate 10-degree nose up position and could see the counterweights below the horizontal stabilizer. I reduced power slowly and kept considerable forward pressure on the stick, which resulted in a 600-800 FPM descent rate with the same AoA and attitude. I was able to maintain roll control and kept wings level. Yaw control was adequate. I made minimal yaw and roll control inputs to avoid a spin and [requested priority handling] with Center, advising loss of control. They asked which airport I requested and I replied I just need to get lower and asked for the freezing level. I observed OAT at 17000 ft. to be approximately 18-20°F and watched it steadily increase as I descended. I found a power setting that would keep the AoA above [the] donut, keeping an adequate IAS while getting 800-1000 FPM descent. At 14000, precipitation was heavy snow and I observed static discharging on the leading edges of the wings via sparks. Around 11000 ft., I was preparing for the elevators to become unfrozen, as I suspected ice had formed and frozen them in position during the slow climb, and was prepared for a rapid nose down movement. The elevators did break loose and I was able to recover the nose down attitude quickly and accurately with the maneuver similar to a power-on stall recovery. While still descending, I commanded several nose up and nose down control inputs with increasing force to ensure controls were still functioning and ensuring I had not broken anything. I then worked with Center to pick my destination and requested lower to get into rain. I observed light to moderate mixed and clear icing at that time on the wings and increased my IAS. Once I was in the heavy rain, the ice melted and the aircraft remained responsive to all controls with the engine performing nominally. I asked and was given vectors for the RNAV XX approach but was only cleared down to 6000 ft. at ZZZZZ, 3000 ft. higher than the approach depicted. Upon reaching 6000 ft. and turning inbound, I was switched to Advisory and was VMC with the field in sight. I executed a 360 turn to lose altitude and then flew the pattern to further reduce altitude, executing a normal landing in heavy rain on Runway XX. I called Center on the phone to cancel IFR. On the ground, I visually inspected all control surfaces, tested trim and autopilot functions, and removed several panels to inspect the control push-rods, finding no abnormalities. I checked weather, refiled, and continued to my destination at a lower altitude. My desire to stay above the tops at night near the upper limits of adequate climb performance resulted in inadvertent flight into icing conditions. I believe the slow, sustained climb resulted in minimal elevator inputs and adequate time for ice to build up on the counterweights, freezing the elevators in place. I believe I had more clear ice than I could observe via flashlight. I should have avoided the situation by either climbing earlier to ensure [that I] remained clear of the clouds or descended into warmer temperatures. I could have also diverted or turned around. I had already flown 6.5 hours for hire in IFR and hazardous weather conditions in the PC-12and fatigue was a factor. I was on supplemental oxygen and remained alert and coherent during the entire event. I credit excellent training – power for altitude, pitch for speed – and upset recovery training during PC-12 initial training, to keeping limited control of the aircraft and avoiding a stall, which would have most likely resulted in a stall/spin and fatal crash.
Time / Day
Date : 202104
Local Time Of Day : 1801-2400
Place
Locale Reference.ATC Facility : ZZZ.ARTCC
State Reference : US
Altitude.MSL.Single Value : 17000
Environment
Flight Conditions : Mixed
Weather Elements / Visibility : Icing
Weather Elements / Visibility : Rain
Weather Elements / Visibility : Snow
Weather Elements / Visibility.Visibility : 10
Ceiling.Single Value : 17000
Aircraft
Reference : X
ATC / Advisory.Center : ZZZ
Aircraft Operator : Personal
Make Model Name : RV-10
Crew Size.Number Of Crew : 1
Operating Under FAR Part : Part 91
Flight Plan : IFR
Mission : Personal
Flight Phase : Cruise
Airspace.Class E : ZZZ
Component
Aircraft Component : Elevator ControlSystem
Aircraft Reference : X
Problem : Improperly Operated
Person
Location Of Person.Aircraft : X
Location In Aircraft : Flight Deck
Reporter Organization : Personal
Function.Flight Crew : Single Pilot
Function.Flight Crew : Pilot Flying
Qualification.Flight Crew : Commercial
Qualification.Flight Crew : Instrument
Qualification.Flight Crew : Multiengine
Experience.Flight Crew.Total : 1625
Experience.Flight Crew.Last 90 Days : 245
Experience.Flight Crew.Type : 294
ASRS Report Number.Accession Number : 1803484
Human Factors : Workload
Human Factors : Fatigue
Human Factors : Situational Awareness
Events
Anomaly.Aircraft Equipment Problem : Critical
Anomaly.Inflight Event / Encounter : Loss Of Aircraft Control
Anomaly.Inflight Event / Encounter : Weather / Turbulence
Detector.Person : Flight Crew
When Detected : In-flight
Result.Flight Crew : Diverted
Result.Flight Crew : Landed As Precaution
Result.Flight Crew : Regained Aircraft Control
Result.Flight Crew : Took Evasive Action
Result.Flight Crew : Requested ATC Assistance / Clarification
Result.Air Traffic Control : Provided Assistance
Assessments
Contributing Factors / Situations : Aircraft
Contributing Factors / Situations : Human Factors
Contributing Factors / Situations : Weather
Primary Problem : Ambiguous
