Now try these — Page 50, Lesson 68

Right, we've finished the theory of centre of gravity and MAC. Now I want you to try some calculations yourself, and then we'll look at how we actually fix a CG that's out of limits. First, the practice problems. These are the book's practice questions — let's try them one at a time. Now, let's move on to the real-world problem: what happens when the centre of gravity is found to be out of limits for any part of the flight? The rule is absolute — the aircraft must not take off until the load has been adjusted so as to bring the centre of gravity into limits. There's no compromise on that. There are two ways to achieve this. The first is by repositioning mass which is already on board the aircraft. This will usually be baggage or passengers — you're simply moving weight from one location to another. The second way is by adding or removing mass. Now, mass that is put on to the aircraft purely for the purpose of positioning or correcting the CG position has a special name — it's called ballast. Here's the key principle: the minimum mass to be moved, or the minimum amount of mass to be loaded or off-loaded, will be that which just brings the centre of gravity on to the nearest limit. So you calculate the smallest change that just touches the limit. Of course, it may be preferable to bring the CG further inside the limits — you're not forced to stop at the boundary, you can give yourself more margin. And there's a critical final check. When the amount of mass adjustment has been calculated, it must be ascertained that this makes the aircraft safe for both take-off and landing. That's the last gate — the adjustment has to be valid for the whole flight envelope, not just one phase.