Although there are limited numbers in passenger service, the 747-400 is still relatively common at cargo airlines, which means there’s also a decent supply chain of spare parts. The CF6 engines which power the LH examples also had a widespread application among several aircraft types, so no real issues there either.

The A340-600, by contrast, is an extremely rare bird. The only application for the Rolls Royce Trent 500 were the A340-500/600 variants, which seems to be Lufthansa’s biggest problem.