Regional Jet 700 ER/LR (CRJ700)
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface; Troubleshooting; Situational Awareness
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Flight Crew Diverted; Flight Crew FLC Overrode Automation; Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory; General Flight Cancelled / Delayed; General Maintenance Action; General Declared Emergency
Aircraft; Weather; Procedure
Enroute; we encountered a runaway STAB TRIM condition. My trainee (PF) accomplished the immediate actions and we then followed up with the Immediate Action Checklist and associated Emergency QRH procedures. We coordinated with ATC to stay out of RVSM airspace while we deviated around thunderstorms. The checklist included 'Land at the nearest suitable airport.' Due to the length of runways and the current weather conditions (thunderstorms) at nearby airports; my Dispatcher and I jointly decided that a major airport was the nearest suitable. Declared emergency with Approach and continued with approach and landing without the use of STAB Trim per QRH procedures. Rest of the flight [to destination] was canceled.  New hire First Officer; thunderstorms; INOP trim and AP. This aircraft had a recent history of STAB Trim issues including at least 6 write ups prior to mine. One of the corrective actions narratives referred to a 'stab motor'. The corrective action was changing of a 'MCU'. I assume this is a 'black box'? I could not find any evidence that the 'motor' was addressed. Upon arrival in the divert airport; I accessed the MDC fault history and noted a 'motor...short...' flag for the time of our event.Six previous write ups related to this failure. Maintenance continues to go for the most cost (short term) effective fix (resets) time and time again. Are these previous write ups related to my STAB Trim Runaway condition?
A CRJ-700 developed a STAB TRIM runaway condition and the new hire First Officer completed the immediate action and QRH procedures. The flight diverted to the nearest airport where an emergency was declared.