Much depends on the specifics of the void, how it was formed, what structures are compromised, particularly control structures, contribution from metal fatigue or other factors, etc., etc., etc.

There have been some spectacularly involved structural failures, with Aloha Airlines 243 perhaps the most impressive of these.

https://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243

Crucially important:

1. No major structural members were involved. The aircrafts main beams run beneath the cabin and cargo floors. As it was, loss of structural integrity of the outer envelope introduced significant additional flex to the airframe which the pilots had to compensate for.

2. No critical control systems were involved. In the Pan Am 103 case, steering cables were severed.

3. There was no internal overpressure or extended hull damage. In AA243, the initial rupture was the result of corrosive metal fatigue and delamination of the outer skin.

I don't disagree with that except modern fly by wire systems involve redundant cabling so it's much harder to cut them all. But, yes if you know the weak points and have unrestricted access a few pounds of High explosive is enough.

The point is without that knowledge and access by the time you have enough HE to take down a modern jumbo jet you can also use it to kill a very large number of people in other ways.

Remember, most bombings are really poorly executed at a technical level. Army's use grenades because they work. If you want to do as much damage to a crowd as possible your better off with a large number of fragmentation grenades than a suicide vest. Create a choke point, detonate something to create a crush, blow up the densely packed crowd.

PS: Mortars are frightfully effective yet tiny.