Narrative:

During preflight; noticed an MEL restriction for a main landing gear door seal; max speed 270 KTS/M.73; the two of us discussed altitude capabilities and buffet zones but; were unable to find the appropriate chart. We contacted dispatch about fuel consumption concerns. Dispatch informed us that they were unable to change the flight plan climb speed and descent speed to 270 KTS but had added 12;000 pounds of fuel for the climb/descent and mild weather deviations; which seemed reasonable.normal takeoff (TOGW of 741.7); ATC cleared us to FL290. While climbing through FL230 we noticed that the vmo and the minimum maneuvering speed (vma) were coming together. As we climbed the vma increased while decreasing the margin of normal operation to approximately a 5 KT window. We stopped our climb at FL230 and requested FL210. We descended to FL210 to increase our safety margin. ATC informed us that the minimum altitude in that area was FL200 due to terrain. We then offset our course 20 miles right to get into an area of lower terrain and received a block altitude of 17;000 ft through FL190. The following are the numbers we saw: FL230: vmo 266 KTS; vma 261 KTS; M.617. FL210: vmo 266; vma 259; M.591. FL190: vmo 266 KTS; vma 244 KTS; M.572.when we were safely established; we began communicating with dispatch. We requested burns to destination at FL190 at M.57 and considered returning to anc or possible diversion. Dispatch returned burns that indicated that we could proceed to our destination considering weather; FL190; terrain clearance; fuel to alternate and a safe amount of fuel on landing. We then spoke to the head of the B747-400 fleet and informed him of our situation and intention to continue to our destination. While enroute we continually updated our position with dispatch. Dispatch updated our burns and landing fuel calculations.we later climbed to FL210 to give ourselves better burn calculations. We continued with only mild weather deviations and landed safely at our destination. It is our belief that this MEL should contain more information about the altitude capabilities of the aircraft while limited to such slow speeds. Dispatch should also have these charts available for reference. The MEL should have at least something to queue the dispatchers and crew into this scenario that we encountered. We also believe that this flight should have been filed over lower terrain and at a lower altitude.

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Original NASA ASRS Text

Title: Dispatched with an MEL Mach/airspeed restriction; a B747-400 flight crew discovered enroute that the speed restriction conflicted with Vma limits except at very low altitudes. Careful coordination with dispatch was required to complete the flight to its destination.

Narrative: During preflight; noticed an MEL restriction for a Main Landing Gear Door Seal; Max speed 270 KTS/M.73; the two of us discussed altitude capabilities and buffet zones but; were unable to find the appropriate chart. We contacted dispatch about fuel consumption concerns. Dispatch informed us that they were unable to change the flight plan climb speed and descent speed to 270 KTS but had added 12;000 LBS of fuel for the climb/descent and mild weather deviations; which seemed reasonable.Normal Takeoff (TOGW of 741.7); ATC cleared us to FL290. While climbing through FL230 we noticed that the VMO and the minimum maneuvering speed (Vma) were coming together. As we climbed the Vma increased while decreasing the margin of normal operation to approximately a 5 KT window. We stopped our climb at FL230 and requested FL210. We descended to FL210 to increase our safety margin. ATC informed us that the minimum altitude in that area was FL200 due to terrain. We then offset our course 20 miles right to get into an area of lower terrain and received a block altitude of 17;000 FT through FL190. The following are the numbers we saw: FL230: Vmo 266 KTS; Vma 261 KTS; M.617. FL210: Vmo 266; Vma 259; M.591. FL190: Vmo 266 KTS; Vma 244 KTS; M.572.When we were safely established; we began communicating with dispatch. We requested burns to destination at FL190 at M.57 and considered returning to ANC or possible diversion. Dispatch returned burns that indicated that we could proceed to our destination considering weather; FL190; terrain clearance; fuel to alternate and a safe amount of fuel on landing. We then spoke to the head of the B747-400 fleet and informed him of our situation and intention to continue to our destination. While enroute we continually updated our position with dispatch. Dispatch updated our burns and landing fuel calculations.We later climbed to FL210 to give ourselves better burn calculations. We continued with only mild weather deviations and landed safely at our destination. It is our belief that this MEL should contain more information about the altitude capabilities of the aircraft while limited to such slow speeds. Dispatch should also have these charts available for reference. The MEL should have at least something to queue the dispatchers and crew into this scenario that we encountered. We also believe that this flight should have been filed over lower terrain and at a lower altitude.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.