Originally Posted by
ethernal
One can argue with precisely how scientific it is, but there is a thread of logic here. The plane cabin has known storage space (underneath seats, overhead bins), and theoretically the standard passenger weights assume that those areas are fully loaded with passenger luggage (at least assuming it is a full flight)..
Cabin baggage is also mostly evenly distributed along the entire length of the cabin, whereas belly baggage may be restricted to certain bins. I’m not sure about the MD90, but for years (and maybe still?), MD88s would frequently be loaded with sandbags closer to the nose to offset weight loaded further back.