Why doesn’t Chad (the country in Africa) import the machine tools and manufacture Aircraft?
Well, it hasn't been 100 years yet.
However, it's still cheaper to buy aircraft than build them, so there's that.
Chad is "close enough" that it doesn't necessarily need to maintain private aircraft. It should be able to maintain State/Military aircraft, but even then, it can contract that out to 3rd parties.
Chad is a TL 8 country like pretty much the rest of the world, even if it lack manufacturing capability.
Simply the economic advantages for the colonies and the survivability alone would make it all but mandatory -- wouldn't it?
Similarly, off world services may be more than enough to service the needs of the world. There's a lot of place on Earth without, say, a gas station, yet they handle vehicle traffic just fine. Those vehicles simply go somewhere else for fuel and maintenance.
However a good example of this was in the TV show "Long Way Round", about a pair of motorcyclists going around the world.
In Mongolia, one of the bikes had a problem, and a local tradesmen tried to fix it. The problem was that it was a "TL 8" motorcycle with a bunch of electronic being worked on by a "TL 7" mechanic. While welding on the bike, he didn't ground something and scrambled the electronics on the bike -- effectively bricking it. He wasn't trying to fix the electronics, the problem was mechanical. But the electricity from the welder zapped the bike electronics.
BUT, what the party did (it was actually 3 people, the 3rd being the camera man) was they bought a local ("TL 7") motorcycle to continue the journey, and had the other one shipped on ahead to "a better starport" to get fixed.
Another anecdote, my Mom bought a used car, and we took it on a road trip. We pulled into Bishop CA (which is at the foot of the Eastern Sierra, and in the middle of the desert) at 2am discovering the clutch gave up the ghost. That derailed our trip abruptly, and we took a bus home. We did that because they had no parts (it was a Ford rebadged Opel, so parts in the US weren't at the local Autozone). They had to order parts for the car. Three weeks later, my Mom took the bus back to Bishop to pickup the car.
Obviously starships are harder to push around and tow through Jump Space, but FRU (field replaceable units) are FRU. It takes mostly mechanical skill more so than detailed engineering knowledge to put the things back together. Although the mechanics in Bishop had never see the car before, they managed to figure out how to replace the clutch. Because, you know, they're mechanics!