Date: 201705
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
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: Dispatcher
Reporter qualification: Dispatch Dispatcher
Human factors: Training / Qualification; Situational Awareness
Anomaly: Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Detector: Person Dispatch
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Manuals; Company Policy
Primary problem: Ambiguous

Narrative: During the briefing for the start of my shift; I was told that the VHHH flight was planned to arrive with about 17.5 on the fuel and the captain was 'nervous.' That seemed like a low arrival fuel for VHHH; especially during the monsoon season. After taking over the desk I checked out the TAF for both VHHH and ZZZZ which was the alternate for the flight. They both had a TEMPO for TSRA in their forecasts that ended at XA00z which was well before the flight's ETA of about XG00z. The flight had been airborne for several hours and I saw that it had been improving on its fuel burn compared to the planned burn and was estimated to land with over 20.0 on the fuel. This flight is notorious for over burning so I kept on eye on the fuel and it continued to improve on its forecast landing fuel.As the flight was coasting in over Russia they asked for an update on the VHHH weather. By that point the VHHH and ZZZZ TAFs had been updated and they now both showed TEMPOs for TSRA until XG00z and VCTS after that. Since that was right at about the flight's arrival time I became concerned about the fuel for those conditions and double checked the release. For the first time I realized that it had been dispatched with special reserves with only 45 minutes of reserve fuel and zero enroute reserves. I was surprised since this required the flight to remain within Class 1 Navigation for the entire route which I didn't think was possible flying over northern Alaska and Russia. I expressed my concerns about the legality of the reserves to the chief dispatcher and several sector managers on the bridge. They were also skeptical about the legality of the reserves. I also told them that the flight might have to be diverted to ZZZZ1 for fuel if the captain and the dispatcher who replaces me felt it was prudent due to VHHH weather.I made a couple of calls to former trainers who told me that the reserves were legal on that particular route based on the company's interpretation of the Special Reserve rules requiring the flight to be able to fix its position at least once each hour using ICAO Class I navigation facilities; per the XXXX exemption. In this case the VORTACs that were used were BRW; RKN; and UTS. I didn't see how this was possible since the service volumes of these VORs were more than an hour apart but was told that the rule was interpreted to allow the aircraft to fix its position at the beginning of the first hour and then at the end of the next hour which effectively allows for nearly two hours of flight between VOR service volumes. If that is the case then the reserves were legal on this route. I looked for this interpretation in writing in the Ops Specs; Dispatch Procedures Manual; and the FM Part 1 but could not find it. I set up a plan with the captain of the flight to re-evaluate VHHH weather prior to the waypoint ZHO and then decide whether to continue on or divert to ZZZZ1 for fuel. I briefed my relief on the plan and my concerns about the reserve fuel. The flight eventually continued on to VHHH and landed without issue.The next day after returning to work I asked a trainer about the interpretation of the Special Reserve rule and he also confirmed that it was interpreted to allow the flight to fix its position at the beginning of the first hour and at the end of the next hour. I asked if this was in writing anywhere and he said to his knowledge it was not. I decided to report it to get a clarification of the interpretation of special reserves fuel requiring a flight to reliably fix its position once each hour using ICAO Class I navigation facilities.There seems to be a lot of confusion in the office about the interpretation of this rule. I talked to a number of dispatchers experienced in dispatching over the Pacific and they were skeptical of the legality of using 45 minutes special reserves on this particular flight; especially since we could not find this interpretation in any of the manuals.




Synopsis: B777 Dispatcher believed the flight he assumed at the start of his shift may have been dispatched illegally with only 45 minutes of reserve fuel on a flight to VHHH.