TECHNICAL FIELD

The disclosure relates to operation of a multi-engine aircraft and, more particularly, to operation of engine air systems for such a multi-engine aircraft.

BACKGROUND

Bleed air produced by a gas turbine engine is compressed air from the compressor stage that is used for engine functions (such as cooling of turbines and to help seal bearing cavities, for example) and is also used for aircraft functions (such as engine starting, cabin pressure, pneumatic systems, pressurizing liquid tanks, etc.). Engine bleed air can be derived from the high pressure or the low pressure compressor stage, depending on the air pressure requirements and the engine operating condition. Low pressure stage air is typically used during high power engine operation, and high pressure stage air may be used during descent and other low power engine operations. Bleed air may be used within an engine for engine functions such as bearing cavity sealing and cooling of various engine components. Improvement is desirable to optimize operation of the efficiency of compressed air systems.

Failure to provide sufficient pressurized air for the engine demands during lower power operation states of an engine can however result in oil seal degradation, oil leakage contamination of cabin air and overheating of air cooled components. Improvement is desirable to monitor and control the delivery of sufficient compressed air for the air demands of engine components when the engine is running in low power operating regimes.

SUMMARY

There is according provided, a method of operating a gas turbine engine having a bleed air system with a switching valve operable to switch between multiple air sources depending on an operating mode of the gas turbine engine, the operating mode including a motive powered mode and a standby mode, the method comprising: operating the switching valve to provide pressurized air from a selected one or more of the multiple air sources to a cavity of the gas turbine engine having seals, and pressurizing the seals of the cavity using the pressurized air; testing the switching valve to determine if the switching valve is functioning normally or abnormally, the switching valve functioning normally when operable to switch between the multiple air sources and functioning abnormally when switching between the multiple air sources is not possible; and if the switching valve is determined to be functioning abnormally, controlling the gas turbine engine to prevent a change of the operating mode thereof.

There is also provided, a gas turbine engine, comprising: a bleed air system including a switching valve having at least first and second air inlets and an outlet in communication with a cavity of the gas turbine engine having one or more seals therein, the first inlet of the air switching valve in communication with a low pressure air source, the second inlet of the air switching valve in communication with a high pressure air source; and a switching valve health monitor, the switching valve health monitor operable to determine if the switching valve is functioning normally or abnormally, the switching valve functioning normally when operable to switch between the first and second inlets, and the switching valve functioning abnormally when switching between the first and second inlets is not possible or the switching valve is otherwise not operating as expected.

There is further provided, a multi-engine aircraft comprising: a first gas turbine engine for providing a first engine power output; and a second engine for providing a second engine power output, the second engine having a bleed air system and an air switching system including: an switching valve having: a low pressure inlet in communication with a first bleed location in a compressor of the second engine; a high pressure inlet in communication with a second bleed location in the compressor of the second engine, the second bleed location being downstream of the first bleed location relative to main gas flow through the compressor of the second engine; and a switch outlet in communication with at least one cavity of the second engine having seals therein; wherein the switching valve is displaceable between at least first and second positions, the first position interconnecting the lower pressure inlet and the switch outlet, and the second position interconnecting the high pressure inlet and the switch outlet; and a switching valve health monitor, the switching valve health monitor including at least one of a pressure sensor and a position sensor operable to determine if the switching valve is functioning normally or abnormally, the switching valve functioning normally when operable to switch between the first and second positions and functioning abnormally when switching between the first and second positions is not possible.

There is also provided a method of operating a gas turbine engine having a bleed air system and a switching valve operable to switch between low and high pressure air source inlets and having an outlet in communication with the bleed air system, the method comprising: actuating the switching valve between a motive powered mode and a standby mode, wherein low pressure compressed air is conveyed to the bleed air system when the switching valve is in the motive powered mode, and wherein high pressure compressed air is conveyed to the bleed air system when the switching valve is in the standby mode; sensing a standby mode pressure using a bleed sensor located downstream from the switching valve; comparing the standby mode pressure to a reference pressure; and when the standby mode pressure is equal to or greater than the reference pressure, maintaining the switching valve in the standby mode; and when the standby mode pressure is less than the reference pressure, actuating the switching valve from the standby mode to the motive powered mode.

In the gas turbine engine as defined above, the control means are adapted, in at least one embodiment, for: before actuating the switching valve from the motive powered mode to the standby mode, sensing the reference pressure comprising an initiation pressure using the bleed sensor located downstream from the valve outlet of the switching valve; and after actuating the switching valve from the motive powered mode to the standby mode, comparing the standby mode pressure to the initiation pressure to determine an initial pressure differential; and when the initial pressure differential is equal to or greater than a downstream reference value, maintaining the switching valve in the standby mode; and when the initial pressure differential is less than the downstream reference value, actuating the switching valve from the standby mode to the motive powered mode

In the gas turbine engine as defined above, the control means are adapted, in at least one embodiment, for: comparing the initial pressure differential to the downstream reference value; and determining a switching valve status being one of: the switching valve is fully open; the switching valve is fully closed; and the switching valve is partially open.

The gas turbine engine as defined above includes, in at least one embodiment: a source sensor located upstream from the high pressure inlet of the switching valve; and wherein the control means are adapted for: before actuating the switching valve from the motive powered mode to the standby mode, sensing the reference pressure comprising a source pressure using the source sensor; and after actuating the switching valve from the motive powered mode to the standby mode, comparing the standby mode pressure to the source pressure to determine a secondary pressure differential; and when the secondary pressure differential is less than an upstream reference value, maintaining the switching valve in the standby mode; and when the secondary pressure differential is equal to or greater than the upstream reference value, actuating the switching valve from the standby mode to the motive powered mode.

In the gas turbine engine as defined above, the control means are adapted, in at least one embodiment, for: comparing the secondary pressure differential to the upstream reference value; and determining a switching valve status being one of: the switching valve is fully open; the switching valve is fully closed; and the switching valve is partially open.

Pressure sensors upstream or downstream from the switching valve can be used to monitor the operation and determine the status of the switching valve. A change in static pressure or the measurement of a pressure differential across the switching valve will provide an indication of whether the switching valve is fully open, fully closed or partially open.

In accordance with embodiments of the present description, malfunction of the switching valve can be detected and can result in aborting of the standby mode operation. Aborting standby mode operation results in a return to the full power motive powered mode to provide sufficient compressed air to avoid engine damage, hazardous or undesirable conditions, such as oil seal degradation, oil contamination of the aircraft cabin air and overheating of air cooled components of the engine.

Further details of these and other aspects of the subject matter of this application will be apparent from the detailed description included below and the drawings.

