Date: 201912
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: Beechjet 400
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Stall Warning System
Component problem: Malfunctioning
Reporter organization: Corporate
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Human factors: Human-Machine Interface
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC Overrode Automation; Flight Crew Regained Aircraft Control
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Leveling at FL400; Stall Warning horn; stall warning light and stick shaker activation occurred. Immediately; added full power and disconnected autopilot for stall recovery procedures and gently lowered the nose to recover. In doing so; lost approximately 600 feet from assigned FL400 but had not locked with autopilot 'alts cap' yet. Immediately advised ATC since the AOA on the pilot's side was at .25 in the green and ISA at +3. Airspeed was not noted since on the left side since I was focused on AOA in the green and we were in a full stall activation and should not be per the computer information. We were getting misinformation by two separate systems and was confusing to diagnose so quickly but priority was to fly the plane and recover from the stall activation. Co-pilot stated they looked at their airspeed at the moment it happened and stated they saw 165 KIAS. We immediately asked for a lower altitude and return back to the departing airport of ZZZ and land. We were given initial vectors and had the airport visually and landed without further control or stall activation. Once on the ground and about one hour later on ground power unit (GPU); went out to the plane and saw the co-pilot side AHRS System failed with red flags. During flight; no flags or failure conditions noted and all systems were working. Good decision for quick stall recovery within 1 minute of stall activation.Crew had good rest and monitoring the aircraft.Crew discussed checklist but nothing in the checklist for this scenario exists and used the checklist for descent; approach and landing. We did not activate emergency services at the airport on landing since we had full control authority and no anomalies.


Second narrative: While airplane was leveling off at ATC assigned altitude of FL400; stall warning horn; stall warning light and stick shaker activation occurred.PIC disconnected autopilot; applied full power and lowered nose. We lost approximately 600 feet doing so. Control of the aircraft was regained promptly.PIC advised ATC immediately and decided to divert back to ZZZ; as we knew the weather was VFR all the way there.I checked airspeed during the warnings and saw it bleeding down and remember seeing 165 indicated.We requested lower altitude and flew back safely to ZZZ without any other issues. We completed all our usual checklists and landed safely.We did not activate emergency services at the airport as we had full control of the aircraft and no abnormalities.About an hour later on the ground the PIC was on GPU and co-pilot side AHRS system was failed with red flags. We did not get any flags or failure or any alerts during flight.I think this failure was handled properly and safely with priority on aircraft control.


Synopsis: BE-400 flight crew reported multiple stall warning indications activated while in cruise. The crew recovered from the stall promptly; noting a disagreement in information from two systems.