We're starting the Mass and Balance portion of your ATPL ground training — Page 125, Lesson 139

We're starting the Mass and Balance portion of your ATPL ground training. This is the index, so I'm going to walk you through the key terms you'll be mastering, and I want you to hear them in the professional language we'll use throughout. First, the foundational concept: Centre of Gravity, abbreviated CG. This is the point about which an aircraft would balance if it were suspended. It's the single most important concept in this entire subject. You'll see it referenced on pages 26 and 29. Closely tied to that is the Centre of Gravity Limits on page 29. These are the forward and aft boundaries within which the CG must lie for the aircraft to be safely controllable. If the CG is outside these limits, the aircraft may not be able to maintain the correct attitude for flight. Now, to actually calculate where the CG is, we use a measurement called the ARM, on page 34. The ARM is the horizontal distance from a reference datum to the centre of gravity of an item. And related to that, we have the Balance Arm on page 30, which is essentially the same concept — the arm of a particular item used in the balance calculation. We also need to define the various masses we work with. Basic Empty Mass on page 31 is the mass of the aircraft plus fixed equipment, unusable fuel, and all operating fluids, but without payload or usable fuel. Then we have Block Mass on page 31, which is the mass of the aircraft ready to start the engines, including the basic empty mass, crew, payload, and fuel. For the fuel itself, we have Additional Fuel on page 65, which is fuel carried in addition to the planned trip fuel. And Alternate (Diversion) Fuel on page 65 is the fuel required to fly from the destination to a designated alternate aerodrome. We also need to understand how the aircraft is loaded. Area Load Limitations on page 58 refer to the maximum load that can be applied to a specific floor area. Cargo Compartments on page 56 are the designated spaces for carrying cargo, and Cargo Handling Systems on page 56 are the mechanisms used to load and secure that cargo. Bulk Cargo on page 56 is cargo that is loaded loose, not in containers or on pallets. We have Baggage on page 71 and Cargo on page 71, which are the two main categories of payload. And there's a specific term, Body Station on page 60, which is a location along the fuselage, measured in inches or millimetres from a reference point, used to define where items are positioned. We also have the CAP 696 on page 29, which is the Civil Aviation Publication that contains the standard load and trim sheet used in the UK. Now, the calculations. We have Calculation of Fuel Mass on page 36, which is converting fuel volume to mass. Calculation of the Basic Empty Mass and CG Position on page 39 shows how to determine the empty aircraft's CG. Calculation of the Loaded Mass and CG Position for Large Aircraft on page 63 is the full process for a transport category aircraft. And Calculations (MRJT1) on page 64 refers to the specific worked examples using the Medium Range Jet Transport, which is the aircraft type we use for these exercises. Finally, we have the Calculating the Underload Using the Formulae on page 64 and Calculating the Underload Using the Load and Trim Sheet on page 66. The underload is the difference between the maximum allowable take-off mass and the actual take-off mass. And that brings us to Allowable Take-off Mass on page 66, which is the maximum mass at which the aircraft is permitted to start its take-off run, considering all operational constraints. There's also a single letter C on page 71, which is likely a reference to a specific item in a load sheet, and the entry CG ON AFT LIMIT, which is a condition you'll check for during your calculations. That's the map of what we're about to cover. Now, let's begin with the very first concept in detail.