Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 100; Flight Crew Total 3300; Flight Crew Type 410
Situational Awareness
Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Flight Crew Regained Aircraft Control
Human Factors; Weather
I was Pilot in Command (PIC) and Pilot Monitoring (PM). First Officer (FO) was Pilot Flying (PF). Forecast called for a possibility of scattered afternoon thunderstorms. Descending on the arrival; ADS-B weather showed scattered small-but-developing thunderstorms. Turned on aircraft weather radar and it showed the same. PIC radar was tilted down and SIC radar was tilted up to get a full picture of the weather. Both ADS-B and radar showed small cells left and right of our arrival route; but nothing directly along our route. No other aircraft had reported turbulence beyond light chop. Below us was an undercast. We turned on nacelle heat and stab/wing heat several minutes prior to entering the cloud layer. We were indicating approximately 300 knots; slowing to 280 knots as required by the arrival. Upon entering the cloud layer; the windscreen was instantly caked in ice and the aircraft was rolled approximately 40 degrees left and pitched nose down. The PF disconnected the Autopilot; established a level attitude; and brought power to idle. After 10-20 seconds the turbulence ended and the flight continued as normal. We made a PIREP of severe turbulence to ATC. After landing we inspected the aircraft and found no visible damage. No injuries occurred. Maintenance was notified. Further inspection revealed no structural damage to the aircraft.I suspect we flew through the top of a developing thunderstorm that was embedded in the undercast; and that had formed quickly enough that ADS-B had not yet shown the cell; and that was below our radar as we approached it; even though my radar was tilted down. This incident just reiterates the need to use extreme caution when flying in the vicinity of convective activity; even if the cells appear 'scattered;' 'small;' and 'weak.'
LR60 Captain reported momentary loss of control after encountering a developing thunderstorm on descent.