SA-227 AC Metro III
Maintenance Airframe; Maintenance Powerplant
Confusion; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Human Factors; Aircraft; Procedure
Maintenance personnel were instructed to [remove and replace] the #1 engine fire bottle that was due for scheduled maintenance. [The] acting lead mechanic called and stated that during the fire bottle change on the aircraft; power was applied and the fire bottle was discharged. Upon investigation it was found that the power and the ground wires on the fire bottle squib had been swapped and the squib was not wired properly. During investigation the mechanic performing the work stated that the wires were pre labeled but the following day when another fire bottle was installed no labels were noted on the wires and a full run down of the wiring print had to take place prior to installing the replacement bottle. Mechanic was counseled on the need to label everything removed no matter how small it may be.
The reporter confirmed that the fire bottle does not have a conventional connector for the squid. It has individual wires that are disconnected and reconnected independently.
Maintenance Technician reported that when electrical power was reapplied following the routine replacement of a Metroliner engine fire extinguisher bottle; the bottle was unexpectedly discharged. He revealed that wires had been incorrectly connected due to mislabeling of the wires.