Date: 201211
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: B777-200
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Fuselage
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Communication Breakdown; Confusion; Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Maintenance
When detected: Other During Maintenance
Result: General Maintenance Action
Contributing factors: Human Factors; Procedure; Manuals; Chart Or Publication; Aircraft
Primary problem: Manuals

Narrative: I was in the forward avionics bay on a B777-200 aircraft and noticed a dried coffee stain in the right-hand (R/H) tunnel area. Apparently; there was a leak from the forward galley into the Lower-41 at one time. The B777 doesn't have any specific reference to address a spill into the lower lobe from the galley. Maintenance Manual (MM) 53-01-01-4 (which pertains to floor board removal and installation) clearly states the dangers of water penetration but there are no references I can find in the B777 Manuals that provide guidance how to handle this scenario.B767 MM 05-51-13 provides detail instructions on how to answer water penetration into the lower lobe. Hence; there is no individual interpretation on how to handle a galley spill on the B767 fleet. I believe the B777 [fleet] should have a similar galley spill reference written in the MM.

Callback: Reporter stated he was in the Right Forward Tunnel of their B777 checking on an expiring MEL deferral during a flight Turn-Around Check. He noticed a coffee stain on the catwalk (floorboards) of the Right Tunnel and determined the fluid had come from the Forward Galley above him. The stain did not indicate the fluid had migrated or traveled beyond the catwalk. There are electronic racks alongside the catwalk; wire harnesses and insulation under the catwalk.Reporter stated they threw water on the Forward Galley floor to see if any fluid would leak down into the Tunnel area. Although no leaks were noted; they did find old sealant with large cracks inside the trash compartment next to the galley carts along the trash compartment floor and sidewalls. Not uncommon for fluid; including coffee; in the trash compartment container to leak through the container onto the compartment floor and drip down into the Lower lobe area. The general feeling was that the trash compartment was the most likely source of the coffee stain. Mechanics re-applied PRC sealant around the trash compartment floor. Reporter stated they did perform an inspection in the Tunnel area prior to departure; similar to what is required for the B767 aircraft if fluid penetration is noted. But the lack of specific language in the B777 Maintenance Manual (M/M) regarding what to do 'after' fluid penetration into the Lower lobe tunnel area has occurred; is a concern. He has not heard from company Engineering about a revision to the B777 M/M addressing the missing procedures.



Synopsis: A Line Mechanic reports about the lack of any specific reference in the B777 Maintenance Manual (M/M) providing guidance on what to do 'after' fluid penetration into the forward Main Equipment Center (MEC) tunnel and lower lobe areas has occurred. Mechanic noted the B767 M/M does provide detailed instructions for similar galley spills.