Now, recording of mass values — Page 17, Lesson 18

We're now into the statistical side of mass and balance — the part where we stop weighing every single passenger and instead use revised standard mass values. Let's start with the weighing machine itself, because the whole survey depends on it. The weighing machine used for passenger weighing must have a capacity of at least 150 kg. That's the minimum it has to be able to measure. The mass must be displayed at minimum graduations of 500 g — so the smallest increment you can read off it is half a kilogram. And the accuracy requirement is tight: the machine must be accurate to within 0.5% or 200 g, whichever is the greater. So if you're weighing a light passenger, the 200 g tolerance governs; if you're weighing someone near the 150 kg capacity, the 0.5% figure is the bigger allowance. Now, recording of mass values. For each flight included in the survey, you must record three things: the mass of the passengers, the corresponding passenger category — that's male, female, or children — and the flight number. So the data isn't just a pile of weights; it's tagged with who they were and which flight they were on. Then we move to checked baggage. The statistical procedure for determining revised standard baggage mass values is basically the same as for passengers, based on average baggage masses of the minimum required sample size. But there are two key differences. First, the relative confidence range — that's the accuracy — amounts to 1% for baggage. Second, you must weigh a minimum of 2,000 pieces of checked baggage. That's a big sample. Now the determination of revised standard mass values. The purpose is safety: to ensure that using these revised standard values, instead of actual weighed masses, does not adversely affect operational safety. So a statistical analysis must be carried out, and that analysis generates average mass values for passengers and baggage, plus other data. Here's where the seat count matters. On aeroplanes with 20 or more passenger seats, those averages apply directly as the revised standard male and female mass values. But on smaller aeroplanes, you must add increments to the average passenger mass. The increments are stepped by seat count: for 1 to 5 seats inclusive, add 16 kg; for 6 to 9 inclusive, add 8 kg; for 10 to 19 inclusive, add 4 kg. So the smaller the aircraft, the bigger the safety margin you pile on top of the average. There's an alternative. On aeroplanes with 30 or more passenger seats, you may apply all adult revised standard average mass values. And revised standard average checked baggage mass values are applicable on aeroplanes with 20 or more passenger seats. Operators also have an option to deviate. You can submit a detailed survey plan to the Authority for approval, and then use a deviating value — provided that deviating value is determined using the procedure in this Appendix. But those deviations must be reviewed at intervals not exceeding five years. Now the male/female ratio. All adult revised standard mass values must be based on a male/female ratio of 80/20 for all flights — except holiday charters, which use 50/50. If an operator wants a different ratio on specific routes or flights, they must submit data to the Authority showing that the alternative ratio is conservative and covers at least 84% of the actual male/female ratios, based on a sample of at least 100 representative flights. Finally, rounding. Average mass values are rounded to the nearest whole number in kg. Checked baggage mass values are rounded to the nearest 0.5 kg figure, as appropriate. So the whole scheme is: weigh a statistically valid sample, compute averages, apply the seat-based increments for small aircraft, enforce the male/female ratio, round appropriately — and you get your revised standard masses that keep the operation safe without weighing everyone every flight.