Date: 201705
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Switch
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
When detected: Aircraft In Service At Gate
Result: General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Procedure; Human Factors
Primary problem: Human Factors

Narrative: The pilot reported in logbook that the right engine fire shutoff push buttons switch guard was loose. I inspected the switch guard and determined that the switch guard must be removed and reinstalled to correct loose discrepancy. At that time; all the required circuit breakers were pulled in accordance with the Aircraft Maintenance Manual (AMM); and all electrical  power was removed from the aircraft. From there; I loosened the switch assembly; and reinstalled the switch guard and re-tightened switch assembly as required by AMM. With aircraft power still off; I then flipped open switch guard and operated switch. Both mechanically checked good. The next step was to ops test the right engine fire shutoff switch; with power on. Aircraft power was turned on; and circuit breakers pushed in to perform ops test; to make sure right engine fire shutoff switch tested good electrically. At that time; I operated the right engine fire shutoff push button switch; and almost simultaneously; bottom frame/bracket on the switch guard; slipped downward over top of the right engine fire bottle push button switch. I then noticed the green light was extinguished on the fire bottle switch; and EICAS display right engine fire bottle low pressure and right fire bottle messages. It was determined that the right engine fire bottle discharge button had been inadvertently depressed; and the fire bottle discharged. I then made a log book entry describing fire bottle discharge and associated EICAS messages displayed. From there; I proceeded to repair the loose switch guard again; using same practices as described previously in this statement. However; upon disassembly of the switch; it was determined that the locking tab on switch; that is pressed against switch housing when tightening; was not in position to ensure complete security of switch. Installing a switch guard usually does not require the complete removal of the switch assembly; unless you can't achieve proper security of switch. The initial installation of switch previously described; did not reveal that the switch was not secure. The second ops test; with power on; however did reveal that the switch was just loose enough to let switch guard slip downward; causing fire bottle deployment. I have [many] years of experience in the maintenance; installation; and repair of Korry switches. I have never experienced where there switch appears to be secure; but becomes loose after a few times of ops checks. My experience is that if the locking tab is not in proper position; the switch will not tighten at all; and switch guard will not hold in place and falls out of place.




Synopsis: CRJ-700 Maintenance Technician reported the engine fire bottle was inadvertently discharged when the fire shut-off switch was tested.