FAR 25.25 Minimum Weight
 

Wondering why the limit, I can understand gust loads over stressing components, anything else?

Took the liberty of reopening your thread, good sir, missed it first time around.

Others may add additional considerations but the first two contenders which come to mind are

(a) gust responses - the lighter the aircraft the rougher it gets.

(b) Vmca has a problem with reducing weight due to the sideways component of the (reducing) lift vector reducing. One keeps in mind the bank limitation.

Thanks John, I cancelled the post after finding the following link which only seemed to talk about CoG and fuel loading. I thought I was somewhat out of my depth, not knowing the ins and outs of the swept wing brethren. Thought there may have been parallels when I went on a 744 twelve hour scenic, no freight, no bags, just a full load of pax, had to carry two tons of ballast to keep CoG in place.

https://www.pprune.org/archive/index.php/t-361135.html

The A300-B4 when converted to cargo had a minimum weight that required some ballast or ballast fuel when empty. This we were told was the lowest weight that the aircraft was test flown at and therefore any lower weight was outside the certification envelope.
This limitation meant that when flying from Sharjah to Stansted empty, a fuel stop was required as around 4 tonnes of fuel was ballast. It took a little while to get ops to understand that if we could load some ballast we could do it non-stop.

The Design Standards (in this case, Part 25, either FAA or EASA) talk a lot about establishing weight limits for which the requirements of the Standards are met. Or, if you prefer, to show compliance with the Standards. To answer the question would need some knowledge of any particular certification program and so on. Not necessarily a simple exercise to establish an answer for any given Type/Model.

It took a little while to get ops to understand that if we could load some ballast we could do it non-stop.

Sometimes you just have to cry a little bit - we can but try .....

Routine loading system restrictions and considerations are in a different basket. For this story, we are concerned with whatever might be the limiting certification design issues ....

The CG position is also relevant here.

It's possible that an empty aircraft is at the limit of the acceptable CG range. If the designer were to "allow" an even lower weight, it may have to expand the acceptable CG range and doing so has all sorts of cascading consequences.

Fokker 50 needed a few hundred kilos in the back on empty flights. Also, don't see a lot of Zappa fans your age...

hehehe, might need to hide my age...