Turbine over-speed brake for hybrid electric gas turbine engine

1. An engine system of an aircraft, the engine system comprising:

a gas turbine engine comprising at least one spool and at least one electric machine operably coupled with the at least one spool; and

a controller configured to:

detect if the at least one spool of the gas turbine engine is in or is approaching an overspeed condition;

shutoff a flow of fuel to the gas turbine engine; and

apply a load to the at least one spool via the at least one electric machine after shutoff of the flow of fuel.

2. The engine system of claim 1 , wherein the controller is further configured to monitor a parameter of the at least one spool and compare the parameter of the at least one spool to an overspeed threshold.

3. The engine system of claim 2 , wherein the parameter is a rotational speed of the at least one spool.

4. The engine system of claim 2 , wherein the parameter is a rate of acceleration of the at least one spool.

5. The engine system of claim 2 , wherein application of the load to the at least one spool is performed when the parameter is equal to or exceeds the overspeed threshold.

6. The engine system of claim 1 , wherein the at least one electric machine is configurable between a motor mode and a generator mode, and the at least one electric machine is configured to apply the load to the at least one spool when in the generator mode.

7. The engine system of claim 1 , wherein the at least one spool includes a low spool and a high spool and the at least one electric machine includes a low spool electric machine operably coupled to the low spool, and a high spool electric machine operably coupled to the high spool.

8. The engine system of claim 1 , wherein the controller is further configured to connect at least one energy sink to the at least one electric machine to apply the load to the at least one spool.

9. The engine system of claim 8 , wherein the at least one energy sink includes one or more of a battery, a capacitor, and an anti-ice/deicing system.

10. A method for limiting overspeed of a spool of a gas turbine engine comprising:

measuring a parameter of the spool;

determining if the spool is in an overspeed condition or is approaching an overspeed condition in response to the parameter; and

upon determining that the spool is in the overspeed condition or is approaching the overspeed condition, shutting off a flow of fuel to the gas turbine engine and applying a load to the spool via an electric machine, wherein applying the load to the spool occurs after shutting off the flow of fuel.

11. The method of claim 10 , wherein measuring the parameter of the spool further comprises measuring at least one of a rotational speed of the engine spool and a rate of acceleration of the engine spool.

12. The method of claim 10 , wherein determining if the spool is in an overspeed condition or is approaching an overspeed condition in response to the parameter further comprises comparing the measured parameter with an overspeed threshold.

13. The method of claim 10 , wherein applying the load to the spool via the electric machine further comprises configuring the electric machine in a generator mode.

14. The method of claim 13 , wherein applying the load to the spool via the electric machine further comprises connecting at least one energy sink to the electric machine.

15. A method for limiting overspeed of a spool of a gas turbine engine comprising:

detecting a failure of a shaft of the spool;

determining a loading of the failed shaft;

applying another load to the failed shaft via an electric machine if the loading on the failed shaft is less than a load threshold; and

determining a position of the failure of the shaft relative to a thrust bearing, wherein the applying another load to the failed shaft is based in part on the position of the failure of the shaft.

16. The method of claim 15 , wherein the spool further comprises a compressor, a fan, and a turbine operably coupled the shaft, and determining the loading of the failed shaft further comprises determining if at least one of the fan and the compressor is applying a load to the failed shaft.

17. The method of claim 15 , further comprising applying the another load to the failed shaft when the position of the failure of the shaft is fore of the thrust bearing.