Not every aircraft has all the expertise, tools, and spares on board at all times to be able to service or replace their engines in flight. If the system has n

Not every aircraft has all the expertise, tools, and spares on board at all times to be able to service or replace their engines in flight. If the system has not been designed from the ground up for that type of service, then the on-board expertise would also have to be gifted at developing workarounds on-the-spot that reliably work the first time.