The 170 or 77kg is the standard weight per passenger for loading unless you actually weigh the passengers.
In Oz, there has been some discussion on categories, as on smaller aircraft, there is a larger risk of overloading..
The use of one standard passenger weight for all aircraft can result in a high probability of overloading.
7. The practice in Australia has been to use the same standard passenger weight, irrespective of the size of the aircraft. However, this practice increases the probability of overloading the aircraft as passenger capacity decreases, and vice versa.
8. For example, when a standard weight of 77 kg is used in a 12 passenger aircraft instead of actual weights, the statistical probability of overloading the aircraft is as high as 25%. This probability diminishes to 0.0014% if the same standard weight of 77 kg is used on a very large capacity aircraft, such as a 400 passenger Boeing 747.
From the FAA, the weights are different, but include clothing weights and a 16lb carryon baggage..
