Beechjet 400
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Troubleshooting; Situational Awareness; Workload
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; Flight Crew Diverted; Flight Crew Requested ATC Assistance / Clarification
Human Factors; Weather; Aircraft
When cruising at FL350 and deviating right of course for thunderstorm avoidance on a heading of 075 we began to encounter blow off and overhangs from other cells in the area reducing visibility to IMC. ATC was overwhelmed and could not give us requested higher altitude and due to high traffic in the area we did not initiate a further deviation right of course until we could ask ATC. Our radar was operating and being manipulated by the Captain showing no cells along our route of flight. We did not realize our radar had failed (no cockpit indications) and suddenly we were in a extreme thunderstorm cell. Our altitude deviated considerably 1;500 feet up and 700 feet down from FL350. We encountered light hail extreme precipitation and severe turbulence. Upon exiting the cell we immediately flew towards clear air and made the decision to divert to ZZZ. Suspecting possible negative G limits had been exceeded and concerned about possible aircraft damage. ATC was able to immediately accommodate our diversion and I landed on runway XX at ZZZ without further issue. The radar and possible turbulence damage was written up in the maintenance log and the company notified according to SOPs and Op Specs. Ensure all radars are operational and checked regularly by Maintenance. Also release this incident to the entire pilot group so that they are aware of this possible issue when operating near thunderstorms.
First Officer reported the aircraft weather radar failed in heavy weather and the flight crew elected to divert to a precautionary landing.