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/north) 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.

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Original NASA ASRS Text

Title: 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.

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.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.