Date: 201811
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Icing
Light: Night
Aircraft: PC-12
Operator: Air Taxi
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Cruise
Aircraft component: Propeller Ice System
Component problem: Failed
Reporter organization: Air Taxi
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Commercial
Human factors: Troubleshooting
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Result: Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Flight Cancelled / Delayed
Contributing factors: Aircraft; Weather
Primary problem: Aircraft

Narrative: Departed ZZZ on IFR flight to ZZZ1 as first leg of a reposition. Deice systems were inspected on the ground and tested prior to departure with no apparent failures. Boots and prop heat were activated upon entering icing conditions in cruise and both failed within a few minutes. OAT was within boot operation limits. Ran appropriate checklists and were unable to clear the failures. We elected to divert initially selecting ZZZ2. In the descent to ZZZ2 we discovered that our EFBs (electronic flight bags) did not have any approach procedures for the area downloaded. ZZZ2 showed VFR conditions so we attempted a visual approach but were unable to find the airport beacon light. ATC issued delay vectors while we worked on a new plan. It appeared that ice accumulation had stopped and that the layer of rime ice accumulated in cruise had been removed; but the OAT was still below freezing and we were still encountering precipitation and clouds. At this point we [advised ATC] and opted to land at ZZZ3. Upon nearing ZZZ3 It became clear that a visual approach was not going to be possible so we copied the RNAV RWY XX Approach at ZZZ3 from ATC and successfully completed the approach. After shutdown we discovered a layer of clear ice on the wings behind the boots that had not been visible in flight.


Second narrative: Deice equipment tested on ground prior to departure with no issue. During cruise; light ice was encountered; and plane was configured appropriately. De-ice boot  message appeared; and was troubleshooted; but could not be rectified. Propeller deice failed shortly after; was troubleshooted; and could not be rectified. ATC was notified to coordinate descent out of icing conditions. Conditions persisted in descent; and decision was made to divert as altitude in positive temperatures could not be established. Vectors were given for ZZZ2; but airport lights could not be confirmed as on in marginal conditions.  New vectors were given for approach into ZZZ3. Approach assisted in vectors onto course as EFB issue (unable to pull up approach plate) prevented standard ID of approach. Landing was safely achieved and flight was terminated and calls were made to Dispatch; Director of operations; and Maintenance. Crew believed aircraft to be free of ice on approach descent through visual inspection. Upon landing; patches of clear ice were found on the top of each wing behind the boots. Boots were clear of ice on approach and upon landing.


Synopsis: Air taxi pilots reported that after entering icing conditions; the boots and propeller heat failed. Pilots diverted and during postflight discovered clear ice on the wings.