Right, let's pick this up — Page 38, Lesson 54

Right, let's pick this up. We've established the dry operating mass and the dry operating index, and now we're looking at how we actually build up the load for a real flight. The first thing I want to stress is the fuel. We said the dry operating mass excludes fuel, so when we add fuel, we need its mass. And to get that mass, we need to know the fuel's density and its specific gravity. That's the ratio of the fuel's density to the density of water. So the mass of the fuel isn't just a number we guess — it's derived from those two properties. Now, for the passengers and baggage, we have a choice. We can use the actual mass — actually weighing them — or we can use the standard masses given in the tables in EU-OPS 1, Subpart J. That's the expedient alternative. It saves time because we don't have to weigh every single person and bag on every flight. But here's the key contrast: we can't normally apply standard mass tables to freight. Freight varies too much from flight to flight, so in general, all freight has to be weighed. There is an exception — an operator can apply to the CAA for permission to produce and use standard mass tables for freight — but that exception is not part of the EU examinations syllabus, so you don't need to worry about it for the exam. Now, let's talk about how we build the whole picture. For light aircraft, we use the BEM — the basic empty mass — and its CG position as the foundation. Everything else, all the other mass and CG requirements, are determined from that. Larger aircraft are different. They have additional mass and CG limits to comply with, and they use a Load and Trim Sheet. That sheet incorporates the DOM — the dry operating mass — as its basis, to simplify and standardize the process. So the light aircraft starts from BEM, the larger aircraft works from DOM on the Load and Trim Sheet. There's one more refinement 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 — providing the requirements of EU-OPS 1, Subpart J are met. So instead of weighing every aircraft individually, you can use one average figure for the fleet, as long as you satisfy that regulation. Finally, we come to the Minimum Equipment List — the MEL. The 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. So it's the absolute minimum that has to be working before you can go. As an example, an aeroplane with three engines would be permitted to fly, in some circumstances, with only two engines operable. Now, the MEL serviceable equipment requirements vary according to the climatic and environmental conditions that exist in various theatres of the world. So what's acceptable in one region might not be in another. And the aircraft operator extracts from the MEL those limitations applicable to his or her aircraft, and enters them into the Aircraft Operating Schedule. That's how the MEL gets translated into the operator's day-to-day rules. Let me show you the flow of all this on the definitions diagram. So to tie it together: we start with the dry operating mass, we add the fuel — whose mass comes from density and specific gravity — we add the traffic load, which is passengers and baggage using either actual or standard masses, and freight which must be weighed. The light aircraft builds from BEM, the larger aircraft uses the Load and Trim Sheet from DOM, and the MEL sets the floor for what equipment must be serviceable before that aircraft is allowed to fly.