Date: 201409
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: Marginal
Light: Night
Aircraft: Beechjet 400
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Descent
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Reverser Lockout
Component problem: Malfunctioning
Reporter organization: Corporate
Reporter function: Pilot Not Flying; First Officer
Human factors: Workload; Time Pressure; Distraction; Situational Awareness
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While in a Center issued descent and in a small (ten degree) turn to the left to join another vector for an ILS approach; the plane suddenly and violently banked 45 degrees toward the right and pitched down slightly. We were passing through approximately 4000' and the power was at idle to slow from 220 to a newly assigned airspeed of 180 with the autopilot coupled on the left during the Captain's leg. The rapid drop toward the right was accompanied with a noise similar but louder to speed brakes being extended at high speeds. I had time to see a Master Warning flasher illuminate and a 'R TR ARM' illuminate; both briefly. I never saw the Master Warning that was associated with the flasher. The whole event lasted approximately 2 seconds and conditions returned to normal. We monitored systems; continued the approach; kept both power levers just forward of flight idle until landing flare and landed without incident.

Callback: The reporter stated his crew had flown that aircraft the previous four days without incident. This event was totally unexpected and the violence of the roll was alarming. The aircraft was pitched about 5 degrees down in a 10 degree left turn; when within a second to second and half it was in a 45 degree right bank accompanied by a noticeable rumble. Very shortly thereafter with the autopilot off and thrust reverser stowed they regained control. This aircraft has standard hydraulic thrust reverser actuator lockout; and the thrust lever wheels on the ground lock out. The crew did not see any anomalies which would explain the apparent momentary thrust reverser inflight activation but the reporter is fairly certain he saw R TR ARM accompanied by the Master Caution Light.Maintenance MELed the right thrust reverser and mechanically locked it closed.

Second narrative: During arrival we were issued a descent from 4000' to 2500' a speed reduction from 230 to 180 and a 10 degree turn to the left. I initiated the turn; descent and speed reduction. Just after the aircraft began to descend at idle power the plane rolled briefly 45 degrees to the right for approximately 2 seconds. The right TR ARM [Thrust Reverser] light briefly flashed as did the master warning. The annunciations cleared quickly and we flew a normal approach. We were never off our assigned heading or altitude during the event.


Synopsis: A BE-400 R Thrust Reverser ARM and Master Warning flashed momentarily during descent accompanied by a violent 45 degree right roll and loud rumbling noise. The whole event lasted approximately 2 seconds and conditions returned to normal. The approach was continued to a normal landing.