Let’s pick this up right where the regulation leaves off — Page 12, Lesson 12

Let’s pick this up right where the regulation leaves off. We’re inside the fleet mass and CG evaluation rules, and I want to walk you through the tolerances and how you actually use fleet values in day-to-day operation. First, the tolerance criteria. If you weigh an aeroplane, or if you calculate the dry operating mass of an aeroplane that belongs to a fleet, you compare it against the established fleet values. The rule is: if the dry operating mass varies by more than ±0.5% of the maximum structural landing mass from the established dry operating fleet mass, that aeroplane gets omitted from the fleet. Same for the CG position — if it varies by more than ±0.5% of the mean aerodynamic chord from the fleet CG, it’s out. So you have two separate tolerances, one for mass, one for CG, and each has its own ±0.5% limit. The mass tolerance is referenced to the maximum structural landing mass, and the CG tolerance is referenced to the mean aerodynamic chord. If an aeroplane exceeds either one, it cannot stay in that fleet. But the regulation does allow you to establish separate fleets, each with its own differing fleet mean masses. Now, there’s a nuance in subparagraph (B). Suppose the aeroplane’s mass is within the dry operating fleet mass tolerance, but its CG position falls outside the permitted fleet tolerance. In that case, you may still operate it under the applicable dry operating fleet mass — so you keep the fleet mass value — but you must use an individual CG position for that aeroplane. So the mass stays fleet-based, the CG becomes individual. Then subparagraph (C) covers a physical difference. If an individual aeroplane has, compared with the other aeroplanes of the fleet, a physical, accurately accountable difference — for example, a galley or seat configuration — and that difference causes the fleet tolerances to be exceeded, the aeroplane may still be maintained in the fleet, provided that appropriate corrections are applied to the mass and/or CG position for that aeroplane. So you don’t necessarily kick it out; you correct for the difference. Subparagraph (D) is a special case. Aeroplanes for which no mean aerodynamic chord has been published must be operated with their individual mass and CG position values, or they must be subjected to a special study and approval. So if you don’t have a published MAC, you can’t use fleet CG values — you go individual, or you get a special study approved. Now let’s move to the use of fleet values, subparagraph (iii). After the weighing of an aeroplane, or if any change occurs in the aeroplane equipment or configuration, the operator must verify that this aeroplane falls within the tolerances specified in subparagraph 2(ii) — the ones we just covered. So every weighing, and every equipment or configuration change, triggers a verification against those tolerances. Then subparagraph (B) handles aeroplanes that have not been weighed since the last fleet mass evaluation. They can still be kept in a fleet operated with fleet values, provided that the individual values are revised by computation and stay within the tolerances defined in subparagraph 2(ii). So you recompute the individual values, and as long as they remain within tolerance, you keep using fleet values. But if those individual values no longer fall within the permitted tolerances, the operator must either determine new fleet values that fulfil the conditions of subparagraphs 2(i) and 2(ii), or operate the aeroplanes not falling within the limits with their individual values. So you have two options: re-establish the fleet, or go individual for the outliers. Let me tie the whole logic together. The fleet concept works because you can average out small variations. The ±0.5% tolerances define how much variation is acceptable. If an aeroplane exceeds the mass tolerance or the CG tolerance, it’s omitted — unless it’s a physical, accountable difference you can correct for, or unless only the CG is out while the mass is in, in which case you keep the fleet mass but use an individual CG. And if you have no published MAC, you’re on individual values or a special study. After any weighing or configuration change, you verify. For aeroplanes not re-weighed, you recompute and verify computationally, and if they fall out, you either re-establish the fleet or go individual. That’s the complete tolerance and fleet-value framework.