Let’s pick this up right where the fuel density idea leaves off — Page 38, Lesson 54

Let’s pick this up right where the fuel density idea leaves off. You’ve got the density and specific gravity of the fuel known — that’s what lets you convert a volume of fuel into a mass, and that conversion is the whole point of knowing those two properties. Now, for passengers and baggage, you have a choice. You can use the actual mass — weigh every person, weigh every bag — or you can use the standard masses given in the tables in EU-OPS 1, Subpart J. Those standard masses are an expedient alternative. Expedient means it’s the quick, practical route: you don’t weigh everyone, you just apply the published average values. But note the legal source — EU-OPS 1, Subpart J is the regulation that lays those tables down. Freight is different. It is not normally possible to apply standard mass tables to freight, because freight varies so much from flight to flight. One day it’s a pallet of steel, the next it’s a crate of feathers — the variation is too great for a standard figure to be safe. So, in general, all freight has to be weighed. There is an exception: in certain circumstances an operator can apply to the CAA — the Civil Aviation Authority — for permission to produce and use standard mass tables for freight. But I’ll flag this for you now: that exception is not part of the EU examinations syllabus. So you need to know it exists, but you won’t be examined on the detail. Now let’s talk about how different aircraft approach this. Light aircraft use the BEM and the CG position as the foundation from which all the other mass and CG requirements are determined. BEM is the Basic Empty Mass — the mass of the aircraft as it stands, empty of payload and fuel, with the standard equipment and unusable fuel included. And CG is the centre of gravity — the point about which the aircraft would balance. For a light aircraft, you start from that BEM and that CG position, and you build everything else on top of it. Larger aircraft have additional mass and CG limits to comply with. They don’t just work from the BEM — they have more constraints. And to handle that complexity, they use a Load and Trim Sheet. That sheet incorporates the DOM as a basis — DOM is the Dry Operating Mass, the mass of the aircraft ready for operation but without traffic load and without fuel. The Load and Trim Sheet simplifies and standardizes the process. So instead of doing the arithmetic from scratch every time, the crew works through a standardized sheet that starts from the DOM. There’s one more option for operators who run a fleet. If you have a fleet of aeroplanes of the same model and configuration, you may use an average DOM and CG position for the whole fleet — one set of figures applied across all the aircraft — providing the requirements of EU-OPS 1, Subpart J are met. So the regulation permits that averaging, but only under those conditions. Now, a completely different document: the Minimum Equipment List, or MEL. An aeroplane manufacturer must produce an MEL for each of their aircraft types. The MEL defines, amongst other things, the minimum level of serviceable usable equipment the aircraft must have prior to flight. Serviceable means it works; usable means it can actually be used. So the MEL sets the floor — the least equipment that must be functioning before you’re allowed to take off. Here’s the classic example: an aeroplane with three engines would be permitted to fly, in some circumstances, with only two engines operable. That sounds alarming, but it’s exactly what the MEL is for — it tells you which items can be inoperative and still allow a safe dispatch. The MEL serviceable equipment requirements vary according to the climatic and environmental conditions that exist in various theatres of the world. Theatres here means regions of operation. So the MEL isn’t a single fixed list — what’s required in the tropics differs from what’s required in the Arctic, because the environment changes the risk. Finally, the operator’s role: an aircraft operator will extract from the MEL those limitations applicable to his or her aircraft and will enter them into the Aircraft Operating Schedule. So the manufacturer writes the MEL, and the operator takes the relevant parts and puts them into their own operating document — the Aircraft Operating Schedule — which then governs how that operator actually runs the aircraft. Let me show you the flow of all this on the definitions diagram. And here’s what a weighing schedule looks like — this is the practical document you’d use to record the actual masses. So to tie it together: you’ve got the fuel density and specific gravity for converting fuel volume to mass; you’ve got standard masses for passengers and baggage from EU-OPS 1 Subpart J, but freight must generally be weighed; light aircraft build from BEM and CG, large aircraft use a Load and Trim Sheet based on DOM; fleets can average DOM and CG under Subpart J; and the MEL sets the minimum serviceable equipment, which the operator adapts into the Aircraft Operating Schedule. That’s the full picture of how mass and balance data is gathered and governed.