Date: 201504
Local time of day: 1801-2400
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Time Pressure
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Pre-flight
Result: Flight Crew Became Reoriented
Contributing factors: Company Policy; Manuals
Primary problem: Ambiguous

Narrative: My route of flight included high terrain along [airway] UR640. In operations; I reviewed the Terrain Critical Depressurization Procedures with my crew to comply with the FOM requirement for terrain avoidance planning.[The South American Procedures Manual] provides a Terrain Critical Depressurization Procedures (TCDP) for UR640. This chart is located under Terrain Critical Depressurization Procedures section of the company manual. The company Depressurization Escape Routes; do not provide guidance for UR640 and there are no Pilot Bulletins that provide terrain avoidance procedures for this route. The Special Authorization (SA) Manual has a note: 'These procedures are valid for the following aircraft only' [Our model of] 777 is not included in the list. My first officers determined that the 777 could use the diversion airports named in the procedure. Since we were not able to find a specific procedure for the this 777-200 model; I contacted our dispatcher; for his thoughts.We reviewed the manual and the note. He initially told me that a TCDP was not required for the [our] model because the airplane had higher performance and longer lasting passenger Oxygen generators. However; I mentioned that I needed a procedure to comply with the FOM planning requirement. I asked him to connect us to the Duty Manager; and we reviewed the chart and the note. He asked me and the Dispatcher to hold while he located a subject matter expert. While we were on hold; I discussed other options with my crew. We discussed using a different route. My relief pilot with several years of [this 777] model experience; told me that he was instructed that a TCDP was not required in South America for [this] 777 model. He repeated the same explanation that I heard from the Dispatcher.My other first officer and I have a long history. We have flown many trips to South America destinations in the B-767. He and I questioned how engine and oxygen generator performance could affect an emergency descent into mountainous terrain.Shortly thereafter; the Duty Manager introduced me to the 777 Fleet Technical Manager. He told me that the C model had higher idle thrust during our drift down and 14 minute oxygen generators. I recognized that we were not communicating my concern. I told him that the emergency descent checklist would include a very high rate of descent and not a drift down.  After a few minutes of discussion; he recognized that I was not concerned with a drift down but with a high dive into high terrain. Now that we were in the same mindset; I re-stated my question; 'Can I use SA manual chart for [this] 777 model?' We reviewed the note again.I needed to move beyond this concern to ensure an on time departure; so I suggested that the Dispatcher file my flight on a different route to avoid the high terrain. The Duty Manager suggested that the procedure could be used rather than change routes. The Fleet Technical Manager agreed that I could use the SA manual chart.I appreciated everyone mentioned in this report. Everyone communicated to me in a very professional manner and I believe they gave me their best guidance for a safe operation. We came to a conclusion that allowed us to safely operate my flight to Houston.




Synopsis: A B777 Captain does not believe that the Company Terrain Critical Depressurization Procedures apply to flight along UR640 and may not apply to the model B777 being flown. After discussions with the Dispatcher and the Fleet Technical Manager the flight departs with unstated alterations to the route of flight.