Air system switching system to allow aero-engines to operate in standby mode

1. A method of operating a multi-engine aircraft having two or more gas turbine engines, the method comprising:

in flight, operating a first engine of the gas turbine engines in a powered mode to provide motive power to the aircraft by driving a common rotatable load;

in flight, operating a second engine of the gas turbine engines in either a powered mode to provide motive power to the aircraft by driving the common rotatable load or in a standby mode to provide substantially no motive power to the aircraft;

when operating the second engine in the powered mode, bleeding pressurized air from a first bleed location of a compressor section of the second engine;

when operating the second engine in the standby mode, bleeding pressurized air from a second bleed location of the compressor section of the second engine, the second bleed location of the compressor section being downstream of the first bleed location relative to main gas flow through the compressor section of the second engine; and

fluidly connecting either the first bleed location or the second bleed location to a bleed air system of the second engine, the bleed air system supplying the pressurized air to one or more components of the second engine in need of pressurized air.

2. The method according to claim 1 , further comprising, in flight, switching the second engine between the powered mode and the standby mode.

3. The method according to claim 2 , wherein the switching of the second engine between the powered mode and the standby mode includes fluidly interconnecting an inlet of the bleed air system with the first bleed location or the second bleed location.

4. The method according to claim 3 , wherein the fluidly interconnecting of the inlet of the bleed air system with the first bleed location or the second location includes operating an input selector switch of the bleed air system.

5. The method according to claim 1 , further comprising reducing fuel consumption of the multi-engine aircraft by switching, in flight, the second engine from the powered mode to the standby mode.

6. The method according to claim 1 , further comprising supplying the pressurized air bled from the first bleed location to the bleed system of the second engine during the powered mode.

7. The method according to claim 1 , further comprising maintaining the pressurized air from the bleed system within the second engine during the standby mode and the powered mode.

8. The method according to claim 7 , wherein the supplying of the pressurized air to the one or more components of the second engine in need of pressurized air includes pressurizing seals and/or cooling turbines of the second engine with the pressurized air.

9. The method according to claim 1 , further comprising maintaining a power output differential between the first engine operating in the powered mode and the second engine operating in the standby mode, defined as a percentage of a second engine power to a first engine power, of between 20% and 95%.

10. The method according to claim 1 , further comprising, when operating the second engine in the standby mode, maintaining a rotational speed of the second engine in the range of 40 to 70% of a rotational speed of the first engine operating in the powered mode.

11. The method according to claim 10 , further comprising switching the second engine from the powered mode to the standby mode by: opening an actuated valve within a high pressure inlet of the second engine to automatically close a normally open check valve within a low pressure inlet of the second engine.

12. The method according to claim 11 further comprising:

sensing the second engine power output and the first engine power output; and

communicating an open signal to the actuated valve when the motive power output differential is below a threshold value.