Regional Jet 200 ER/LR (CRJ200)
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Procedure
At the ramp 'APU Battery Charger' and 'Main Battery Charger' status messages illuminated. Engines are started; parking brake is still on. I planned to power down briefly.  As we do normal power down every time we shut down the aircraft; I turned off all AC generators first and all the indication was normal except the above messages. Upon turning off the Main Battery switch; the nose gear retracted all of sudden; without any warning or message. Both of the main gears were not retracted and showing the green indications. I asked the Ramp Agent to bring up boarding stair and deplaned the passengers normally.I did not expect the nose gear retraction upon turning off AC power and the Main Battery Switch. I did not expect any threat as the parking brake was not even released.
The reporter stated that the nose gear retraction valve on this particular aircraft was very sensitive and did in fact retract the gear. This was the second similar event with the same anomaly. The valve involved was on this aircraft model's AD list and was replaced after this event. All the Company's aircraft were also checked but no other defective valves were found.
A CRJ200 nose gear retracted at the gate with both engines running after the Captain powered the aircraft down and selected the Battery Switch OFF in order to reset APU and Main Battery Charger EICAS alerts.