Method of operating an aircraft engine and fuel system using multiple fuel types

A fuel system for a gas turbine engine having at least one fuel nozzle open to a combustion chamber, the fuel system comprising:

• a jet fuel subsystem having a jet fuel conduit extending from a first reservoir area to the at least one fuel nozzle across at least one auxiliary system operable using a flow of said jet fuel, at least one fuel delivery system operable to circulate a controlled flow rate of the jet fuel within said conduit and across the at least one auxiliary system, a recirculation conduit branching off from the jet fuel conduit downstream of the at least one auxiliary system, and an actuator valve operable to selectively direct a flow of jet fuel to the at least one fuel nozzle or to the recirculation conduit;
• and
• an alternative fuel subsystem having an alternative fuel conduit extending from a second reservoir area to said at least one fuel nozzle.

An aircraft having a gas turbine engine having a gas turbine engine having at least one fuel nozzle open to a combustion chamber and a fuel system comprising:

• a jet fuel subsystem having a jet fuel conduit extending from a first reservoir area to said at least one fuel nozzle across at least one auxiliary system operable using a flow of said jet fuel, at least one fuel delivery system operable to circulate a controlled flow rate of said jet fuel within said conduit and across said at least one auxiliary system, a recirculation conduit branching off from the jet fuel conduit downstream of the at least one auxiliary system, and an actuator valve operable to selectively direct a flow of jet fuel to the at least one fuel nozzle or to the recirculation conduit;
• and
• an alternative fuel subsystem having an alternative fuel conduit extending from a second reservoir area to said at least one fuel nozzle.