Definitions and Calculations — Page 68, Lesson 88

I want to walk you through the second half of the definitions and calculations chapter. We've already covered running load and area load, so let me make sure you've got those nailed down, because they're the foundation for what comes next. First, running load. We had a box weighing 100 kg, and we looked at it as a 3 ft by 3 ft footprint. But here's the key twist: if you have a box of the same weight, 3 ft × 2 ft × 3 ft, you can orient it so the 2 ft side runs fore and aft. That changes the running load. The running load is the mass per unit length along the aircraft's longitudinal axis. So for that box, you'd calculate 100 divided by 2, divided by 12, which gives you 4.16 kg per inch. The division by 12 converts feet into inches, because the running load is expressed per inch. The point here is that cargo may have to be orientated correctly to prevent exceeding the running load limitations. Orientation is a tool you use to stay within limits. Now, area load. This is the load intensity, which is mass per unit area. For the first box, standing on its 3 ft × 3 ft base, the area is 9 square feet. So the load intensity is 100 divided by 9, which is 11.1 kg per square foot. But the second box, if you place it on its side, measures 2 ft × 3 ft, which is 6 square feet. So the load intensity becomes 100 divided by 6, which is 16.66 kg per square foot. Again, the cargo may have to be orientated correctly to prevent exceeding the distribution load limitations. So you see, both running load and area load are about how you place the cargo to keep the floor and structure within their limits. Now let's move to the calculation of the loaded mass and CG position for large aircraft. This is where things get more complex than for light aircraft. For a large aircraft, the Take-Off Mass, or TOM, and the Zero Fuel Mass, or ZFM, and their respective CG positions are determined by the same method used for light aircraft. But there's one crucial difference: the Dry Operating Mass, or DOM, is used as the starting point, as opposed to the Basic Empty Mass, or BEM. So remember that distinction — for large aircraft, you start from the DOM. The fuel reserves and the traffic load compilation are more complex for a large aeroplane than for a light one. That's why a Load and Trim Sheet is used. It's a document that coordinates the data and simplifies the procedure. Now, here's an interesting operational point: many large aircraft operators do not bother to calculate the landing mass and CG position on the Trim Sheet. Instead, they calculate the ZFM and its CG position. Why? Because should a large aircraft need to divert to another airfield, its actual landing mass could be many tonnes more, or less, than the estimated value, and its CG position could vary considerably from the projected value. But here's the safety logic: assuming that both the TOM and the ZFM, and their respective CG positions, are within limits prior to take-off, they will remain in limits throughout the flight. That's the key principle — if you're within limits at take-off and at zero fuel, you stay within limits for the whole flight, even if you divert. Now, let's talk about compiling a document, specifically the Load Sheet. In its simplest form, a load sheet is a list showing the BEM or DOM and the CG position. Added in tabular form are the elements of the traffic load and fuel, each with their individual masses, arms, and moments. From this list, the take-off mass and CG position can be calculated. So you're building up from the basic empty or dry operating mass, adding traffic load and fuel, each with its arm and moment, to arrive at the take-off mass and CG. A load sheet is individual to each type of aircraft and must be compiled before each flight. It's not a generic form — it's specific to the aircraft type, and it's mandatory for every flight. Now, the regulatory requirement. A load sheet is required by EU-OPS 1 Subpart J to contain some mandatory information. Let me list these for you, because you need to know them cold. First, the aeroplane registration and type. Second, the flight number. Third, the identity of the commander. Fourth, the identity of the person who prepared the document. Fifth, the dry operating mass and CG position. And sixth, the mass of take-off fuel and trip fuel. So those six items are the mandatory content of a load sheet under EU-OPS 1 Subpart J. Let me just recap the key points. Running load is mass per unit length, and you can orient cargo to stay within limits. Area load is mass per unit area, and again, orientation matters. For large aircraft, you start from the DOM, not the BEM. You use a Load and Trim Sheet because fuel and traffic load are more complex. You often calculate ZFM instead of landing mass because of the diversion scenario, and the principle is that if TOM and ZFM are within limits at take-off, they stay within limits throughout the flight. And the load sheet is a mandatory document with six specific items required by EU-OPS 1 Subpart J. One more thing — don't forget there's a conversion chart on page 4 of the data sheets. That's a handy reference for you when you're working through these calculations.