Date: 201202
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Dusk
Aircraft: B737-400
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Fire Protection System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Situational Awareness; Workload; Troubleshooting; Time Pressure; Communication Breakdown; Distraction; Confusion
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
When detected: Aircraft In Service At Gate
Result: General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Environment - Non Weather Related; Aircraft; Company Policy; Human Factors
Primary problem: Human Factors

Narrative: At shift change; [I] received a gate call for a B737 aircraft with numerous items to be addressed. Last item; due to wheel well fault; had to change Fire Control Unit (FCU). Called for paper work; pulled FCU; verified proper Part Number (P/N) to Stores. Part arrived before paperwork arrived. And being pressed for time; had pulled circuit breaker prior to removal; and thought powering down aircraft would negate any electrical power to FCU. Swapped out FCU's and preformed operations check; operations good; then discovered light plate was missing. [I] powered down aircraft battery switch to 'OFF'. While installing light plate had to slightly move APU and #2 engine fire handles for installation of light plate. [I] verified discharge [of fire bottles]. Pilot refused to take aircraft or have an MEL issued for [crew] oxygen (O2) at 1;000 PSI for jump seat riders standing by. [I] serviced O2 to full level. Finished all other maintenance items except FCU; and were at least 30-minute into [departure] delay. Aircraft temporarily taken out of service; and all involved sent for drug and alcohol [tests]. Suggest [that] regardless of delay; wait for paperwork to arrive to start job.

Callback: Reporter stated the FCU he was referring to was actually the Fire Control Panel (FCP) on the P-8 Center Control Pedestal in the cockpit. The original problem started at the gate when the flight crew could not get the B737 aircraft's wheel well warning light to illuminate during their preflight fire warning test. After trouble shooting the fire warning system; he decided to replace the FCP. But the replacement FCP came without the lighted faceplate; which required the transfer of the faceplate from the removed unit to the replacement FCP. That's where their maintenance problems really started.Reporter stated that in the past; replacement Fire Control Panels (FCP) came with the lighted faceplate. But a company decision had been made to not include the lighted faceplate as a cost savings measure. The faceplates are generally heavily gummed up around the edges from old; sticky fluid residue and grimy dirt. The lighted plate has to be removed carefully; not bent and pried; from the FCP or the faceplate will break. Reporter stated when they realized the lighted plate had to be transferred over to the replacement FCP; they decided to go ahead with the transfer; because the paperwork was slow in getting to them. But IF they had the paperwork; they would have seen the Maintenance Manual directions that stated: to either disconnect the electrical connectors on the bottom of the FCP unit; or disconnect the aircraft's battery cables. They had not done either. The electrical connectors on the FCP are very short and difficult to reattach.  Instead they thought that with the battery switch in the 'OFF' position; DC power would be removed from the FCP. But that was not correct. Even with the battery switch 'OFF'; and the electrical connectors still connected; the lighted faceplate was directly connected to the battery 'HOT' BUS through the lighted faceplate's metal contact ring and the FCP unit. So when he moved the APU and #2 engine fire handles on the FCP; to reposition the lighted face plate; the fire bottle squibs fired and discharged the bottles. No damage to the APU or Engine occurred because they were not running at the time. Aircraft was back in service within two hours.



Synopsis: A Line Mechanic reports the APU and #2 engine fire bottles were inadvertently discharged; even with the battery switch 'OFF'; when he was transferring a lighted faceplate from a malfunctioning Fire Control Panel (FCP) to a replacement FCP on the P-8 Center Control console of a B737 aircraft.