Definitions and Calculations — Page 68, Lesson 93

Right, let's pick this up with the fuel state definitions, because they feed directly into the load sheet calculation we're about to do. We've already covered the individual fuel masses — contingency, alternate, final reserve, additional. Now, the take-off fuel for calculations is simply the sum of all those, but excluding the start and taxi fuel. So when we talk about take-off fuel in a mass and balance sense, we're talking about the fuel that will actually be burned in flight, not the fuel sitting in the tanks while we're queuing on the taxiway. And one important note: the fuel state requirements vary with the intended flight plan, and they are not always required. So you don't automatically add every fuel category to every flight — it depends on what the plan calls for. Then we have the landing fuel mass. This is the actual amount of fuel remaining in the tanks at touchdown. In a trip where no eventualities have occurred — meaning nothing abnormal happened, no diversions, no holds — it will include the contingency, alternate, final reserve, and additional fuel masses, if they were included in the flight plan. So the landing fuel is what's left after you've burned the trip fuel and the contingency that you actually used. Now, here's where the Load and Trim Sheet for the MRJT1 does things slightly differently than the method we saw earlier. Instead of determining the lowest traffic load directly, the sheet first determines the allowable take-off mass. Then it calculates the allowable traffic load by deducting the operating mass from that allowable take-off mass. Finally, it calculates the underload by deducting the actual traffic load from the allowable traffic load. So the allowable take-off mass is the lowest of three values. First, the maximum zero fuel mass plus the take-off fuel. Second, the regulated take-off mass. Third, the regulated landing mass plus the fuel used in flight. Let me walk you through the example with the MRJT1 numbers. The maximum zero fuel mass is 51,300 kilograms. The maximum structural take-off mass is 62,800 kilograms. The maximum structural landing mass is 54,900 kilograms. We're assuming no performance limits, so the regulated take-off and landing masses equal the structural limits. The dry operating mass is 34,000 kilograms. The actual traffic load is 12,400 kilograms. The take-off fuel load is 16,000 kilograms, and 8,000 kilograms of fuel was used in flight. So, allowable take-off mass — the lowest of three. First candidate: MZFM plus take-off fuel, that's 51,300 plus 16,000, which equals 67,300 kilograms. Second candidate: the regulated take-off mass, which is 62,800 kilograms. Third candidate: the regulated landing mass plus the estimated fuel consumption, that's 54,900 plus 8,000, which equals 62,900 kilograms. The lowest of those three is 62,800 kilograms — the regulated take-off mass. Now, the maximum allowable traffic load for the conditions prevailing is determined by subtracting the operating mass from the regulated take-off mass. So that's 62,800 minus the operating mass. And the operating mass here is the dry operating mass plus the take-off fuel — 34,000 plus 16,000, which is 50,000 kilograms. So 62,800 minus 50,000 gives us 12,800 kilograms of maximum allowable traffic load. Finally, the underload is determined by subtracting the actual traffic load from the maximum allowable traffic load. So 12,800 minus the actual traffic load of 12,400 kilograms gives us an underload of 400 kilograms. That's the spare capacity we have — we could have carried 400 more kilograms of payload under these conditions. So the key sequence on the sheet is: allowable take-off mass first, then allowable traffic load, then underload. And the underload is the difference between what we could carry and what we actually are carrying.