B727-200
Maintenance Powerplant; Maintenance Inspection Authority; Maintenance Airframe
Maintenance Technician 19
Situational Awareness; Time Pressure; Distraction; Confusion; Communication Breakdown
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Chart Or Publication; Human Factors; Manuals
Flight Engineer (F/E) questioned engine Fire Bottle Weight Check Date; it was one day expired on tag. General Maintenance Manual (GMM) section was found that allowed for Hydrostatic/Acoustic Inspection Overrun to [go to the] next C-Check.  F/E accepted that and no Logbook entry was created. After aircraft departed; Maintenance Control called and they had found a Maintenance Manual (M/M) reference for reweighing the [Fire] bottle if it had no pressure gauge. I had remembered the GMM reference from the older; pressure gauge bottles and automatically went to it under the pressure of [being] close to blockout time.  I also had read of Acoustic Testing to determine contents [weight] of bottles and assumed that applied to the bottles with no gauges. Maintenance Control stopped the aircraft at the hub to have the bottles reweighed.
Reporter stated that he and Maintenance Control were mixing-up the Hydrostatic Test versus the Fire Bottle Weight Check information in their General Maintenance Manual (GMM). Maintenance Control had called him back after finding a Revision notice just as the B727 was lifting off.   Engineering had issued a Revision to their Maintenance Manual (M/M) approximately nine months earlier; requiring fire bottles without pressure gauges had to be weighed prior to dispatch if the Weight Check date on the fire bottle tag had expired. Only a few of their aircraft have Fire Bottles without pressure gauges. The Revision included a procedure using a Laser to check the fire bottle dimensions for weight; which would indicate if any Halon had escaped the bottle.
A Line Mechanic reported a possible illegal dispatch of a B727-200 aircraft after he misinterpreted a Maintenance Manual (M/M) section for an 'Out of Date' Engine Fire Bottle Weight Check requirement.