Date: 201412
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Beechjet 400
Flight phase: Climb
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Fractional
Reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition; General Maintenance Action; General Flight Cancelled / Delayed; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: On climb out; while climbing through about 2000 ft MSL; we got a master warning along with right engine thrust reverser 'Arm' and 'Unlock' light. I was pilot flying; and we verified that the right (Emergency) Emer-Stow button was illuminated and the captain pushed the right side emergency stow. The captain notified ATC of our issue and we were given a vector to a downwind to run our checklist while returning to land at ZZZ. We completed the checklist; declared an emergency; and following the last item on the checklist; to land at our nearest suitable airport; which for us was ZZZ. Captain notified the passengers that we were returning to land. We were vectored to ILS 10L for an uneventful landing.

Callback: Reporter stated the two engines on their Beech Jet 400 XP were Pratt-Whitney PW JT-15D5 turbofans with external clam shell type reversers. The reversers are hydraulically operated and will open fully in about two seconds. There are two emergency-stow buttons for the left and right engine reversers; located at the glare shield on the Captain's side next to the master warning light.Reporter stated the right emergency-stow light did not indicate a re-lock of the right engine reverser after being pushed. So they returned to their departure airport. They did not feel any noticeable vibration during the event. He has experienced additional training in unusual upset attitudes simulating a reverser deploying on Takeoff; the training was quite challenging. If the thrust reverser opens in flight; pilots have to be aware that electric servos will Auto-Retard the throttle on the affected engine when the pilot hits the Emergency Restow button. The affected engine throttle will move aft. Engines do not have FADEC systems. Only direct cable from the throttles to the fuel Hydro-Mechanical Unit (HMU) on the engines. Reporter stated their QRH Checklist procedures directs pilots to slow airspeed; hit the Emer-Stow button and find the closest suitable airport. Maintenance said the event was an indication problem; not an actual reverser unlocking and ready to deploy. A sensor between the light and the engine had faulted. A former marine pilot and one of their trainer's; who had experienced an inflight reverser deployment said he had to use spoilers and rudder to recover before auto-restow of the reverser occurred.

Second narrative: During the climb out on departure off of runway 10L; at approximately 2000 ft MSL; the master warning light illuminated along with the Right Engine Thrust Reverser 'Arm' and 'Unlock' light. I was the pilot monitoring at the time. When I noticed what happened; I immediately pushed the right engine TR (Thrust Reverser) emergency stow button. I notified departure control that we had a problem with the thrust reverser and asked for vectors to complete a checklist. We followed the checklist for TR unlock in flight and I then declared an emergency and asked to return to ZZZ. I then notified the passengers of our emergency condition. We continued the normal checklist and made a normal landing on runway 10L.


Synopsis: During climbout; a Captain and First Officer respond to a master warning light illumination and a right engine thrust reverser 'Arm' and 'Unlock' light on a Beech Jet BE-400XP. The right engine reverser did not indicate Re-lock after the Captain pushed the Right Emergency-Stow button on the glare shield. Crew declared an emergency and returned to departure airport.