B737-800
Flight Crew Air Transport Pilot (ATP)
Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Returned To Gate; General Flight Cancelled / Delayed
Incorrect / Not Installed / Unavailable Part; Aircraft
During engine start; first flight of the day; the aft cabin fire extinguisher began to discharge Halon. Not from the emitter but from the junction of the bottle and the high pressure regulator. The Flight Attendant; who was walking by doing her pre-departure checks; heard the leak; saw the Halon; and used blankets to contain the gas. Returned to the gate and opened forward cabin entry door. The Halon had dissipated by then and; without a replacement extinguisher; the passengers were deplaned. Probably dissimilar metal corrosion between the bottle and high pressure valve combined with a cold night created enough of a gap in the seal. Remove the valves from the bottles and inspect the tolerances. The hydrostatic test may not be sufficient. This failure takes the aircraft out of service.
B737 Captain reported a cabin fire extinguisher leaked out all its pressure.