Definitions and Calculations — Page 68, Lesson 93

Let's pick this up right where the fuel definitions left off. I want to walk you through the exact calculation sequence the MRJT1 Load and Trim Sheet uses to find the underload, because it's a slightly different path than the one we just did by hand. First, a quick recap of the fuel terms we need, because they feed straight into this. The take-off fuel for calculations is simply the sum of the contingency, alternate, final reserve, and additional fuel — but it excludes the start and taxi fuel. And note that these fuel state requirements vary with the intended flight plan; they are not always required. The landing fuel mass is the actual amount of fuel remaining in the tanks at touchdown. In a trip where no eventualities have occurred, it will include the contingency, alternate, final reserve, and additional fuel masses, if they were included in the flight plan. Now, the key difference. Instead of determining the lowest traffic load directly, the Load and Trim Sheet first determines the allowable Take-off Mass. It then calculates the allowable Traffic Load by deducting the Operating Mass from the 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. The first is MZFM plus Take-off Fuel. MZFM is the Maximum Zero Fuel Mass — the maximum mass of the aircraft without usable fuel. The second is the Regulated Take-off Mass. The third is the Regulated Landing Mass plus the fuel used in flight. Let me run the worked example so you see the numbers. For the MRJT1, the MZFM is given as 51,300 kg. The MSTOM — that's the Maximum Structural Take-off Mass — is 62,800 kg. The MSLM, the Maximum Structural Landing Mass, is 54,900 kg. We assume there are no performance limits, so the Regulated Take-off Mass equals the Structural Limited Take-off Mass, and the Regulated Landing Mass equals the Structural Limited Landing Mass. The DOM — Dry Operating Mass — is 34,000 kg. The actual traffic load is 12,400 kg. The take-off fuel load is 16,000 kg, and 8,000 kg of fuel was used in flight. Now we compute the three candidates for allowable Take-off Mass. First, MZFM plus Take-off Fuel: 51,300 plus 16,000 equals 67,300 kg. Second, the Regulated Take-off Mass: 62,800 kg. Third, the Regulated Landing Mass plus the estimated fuel consumption: 54,900 plus 8,000 equals 62,900 kg. The lowest of these three is 62,800 kg — the Regulated Take-off Mass. So that becomes the allowable Take-off Mass. Next, we determine the maximum allowable Traffic Load by subtracting the Operating Mass from the Regulated Take-off Mass. The Operating Mass here is the DOM plus the take-off fuel: 34,000 plus 16,000 equals 50,000 kg. So the maximum traffic load is 62,800 minus 50,000, which equals 12,800 kg. Finally, the underload is the maximum allowable traffic load minus the actual traffic load. That's 12,800 minus 12,400, giving an underload of 400 kg. So the whole chain is: allowable Take-off Mass is the lowest of the three candidates; subtract Operating Mass to get maximum traffic load; subtract actual traffic load to get underload. That's the exact sequence the sheet follows.