Small Transport; Low Wing; 2 Recip Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 1
Situational Awareness
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Weather
While on break I received a page that we had an emergency.  I was told an aircraft had encountered severe icing in a climb from 8;000 to 10;000 feet.  The icing resulted in the aircraft being unable to maintain altitude; dropping from 9;600 to 1;800 within a minute in what appeared a stall.  The aircraft was able to regain control of altitude and diverted to a nearby airport safely without further incident.  The controller who had relieved me stated she did not know there was icing at 10;000 feet.  During our relief briefing; the relieving controller stated she had the S.I.A. and all associated information.  The S.I.A. had a handwritten strip that had been posted by Approach control regarding light to moderate icing from 10;000 to 11;000 feet.  During the relief briefing I told the controller about occasional icing between 11;000 to 14;000; latest reported by a PC12 at 14;000 with trace rime icing.  I had not received any icing reports at 10;000 for some time.  I had an air carrier pass through the same area recently with no reports of icing at 10;000.We have no good way of posting PIREP information in a conspicuous area.  We have a board on one side to put info on; but is rarely used.  Instead; we typically rely on hand written strips for pertinent information.  Would be nice to have an actual IDS4 at each work station.
I was working Approach control.  I was working Aircraft X; he was level at 8;000 and asked to climb to 10;000. There were icing reports at 4;000; also; at 11;000 and 14;000.  I gave the pilot his requested altitude.  I figured it was to get into better flight conditions. Moments later I heard screaming and a mayday call from Aircraft X which was on a rapid descent down.  He recovered around 1;800 feet.  He did declared an emergency during his dive and once he gained control of his aircraft; I verified his altitude and state his intentions.  He landed at the nearest airport cancelled his IFR and reported safely on the ground.I do not have any recommendations at this time.
Two controllers and one pilot report of the aircraft that encounters icing and drops from 10;000 feet to 1;800 feet.