After tremendous work by CodenameJack, and Concorde users "LameLefty" and "RESETXPDR" on the microsoft forums, all of the engine and fuel issues have been diagnosed and fixed. The updates will be sent to Just Flight and the Marketplace today to ensure Concorde gets back into the skies as quickly as possible for all owners.
I should also add that Jorg Neumann at microsoft has been hugely helpful in talking over what went wrong. We were able to find a way to improve the communication between Asobo Studios and third-party developers prior to Sim Update releases, so that all developers know more about what has actually been changed within the sim *before* the final update rolls out. The plan is that with a detailed Changelog in advance of Sim Update releases (but while still in beta), devs can rapidly locate and diagnose issues and prepare their updates with more accuracy, instead of wondering what's a new sim-bug and what's a genuine fix or change each time the updates roll out. This idea is a WIP, as it would require Asobo to lock down their code earlier to give developers more time to make changes, but Jorg liked the idea and hopefully it will become a thing in the future.
Concorde's update should reach users today or tomorrow, depending on where you purchased Concorde.