A gas turbine engine including a turbine drive system, comprising: an engine case; a low pressure compressor, a high pressure compressor, a high pressure turbine and a low pressure turbine disposed in flow series within the engine case, the high pressure compressor and the high pressure turbine mounted on a high pressure spool and the low pressure compressor and the low pressure turbine mounted on a low pressure spool, each spool rotationally mounted within the engine case and configured to rotate at a speed; at least one engine accessory gearbox mounted accessory having an input shaft coupled to the high pressure spool to receive a drive force therefrom; a bleed air conduit having an inlet port, an outlet port, and a flow passage therebetween, the bleed air conduit inlet port fluidly coupled to the high pressure compressor to receive a flow of bleed air from the high pressure compressor; a flow control valve mounted on the bleed air conduit and selectively movable between at least a closed position, in which the bleed air conduit inlet port is fluidly isolated from the bleed air conduit outlet port, and an open position, in which the bleed air conduit inlet port is in fluid communication with the bleed air conduit outlet port; an air turbine having a fluid inlet and a rotationally mounted air turbine output shaft, the air turbine fluid inlet in fluid communication with the bleed air conduit outlet port to receive bleed air therefrom when the flow control valve is in the open position, the air turbine output shaft coupled to the at least one engine accessory gearbox mounted accessory; and a lock-up clutch coupled between the air turbine output shaft and the at least one engine accessory gearbox mounted accessory and movable between (i) an engage position, in which the air turbine output shaft is coupled to the at least one engine accessory gearbox mounted accessory in a first rotational direction and a second rotational direction opposite the first rotational direction, and (ii) a disengage position, in which the air turbine output shaft is not coupled to the at least one engine accessory gearbox mounted accessory, wherein, the lock-up clutch is further configured, in the engage position, to allow the air turbine to respond to changes in the speed of the high pressure spool during both acceleration and deceleration thereof. an engine case; a low pressure compressor, a high pressure compressor, a high pressure turbine and a low pressure turbine disposed in flow series within the engine case, the high pressure compressor and the high pressure turbine mounted on a high pressure spool and the low pressure compressor and the low pressure turbine mounted on a low pressure spool, each spool rotationally mounted within the engine case and configured to rotate at a speed; at least one engine accessory gearbox mounted accessory having an input shaft coupled to the high pressure spool to receive a drive force therefrom; a bleed air conduit having an inlet port, an outlet port, and a flow passage therebetween, the bleed air conduit inlet port fluidly coupled to the high pressure compressor to receive a flow of bleed air from the high pressure compressor; a flow control valve mounted on the bleed air conduit and selectively movable between at least a closed position, in which the bleed air conduit inlet port is fluidly isolated from the bleed air conduit outlet port, and an open position, in which the bleed air conduit inlet port is in fluid communication with the bleed air conduit outlet port; an air turbine having a fluid inlet and a rotationally mounted air turbine output shaft, the air turbine fluid inlet in fluid communication with the bleed air conduit outlet port to receive bleed air therefrom when the flow control valve is in the open position, the air turbine output shaft coupled to the at least one engine accessory gearbox mounted accessory; and a lock-up clutch coupled between the air turbine output shaft and the at least one engine accessory gearbox mounted accessory and movable between (i) an engage position, in which the air turbine output shaft is coupled to the at least one engine accessory gearbox mounted accessory in a first rotational direction and a second rotational direction opposite the first rotational direction, and (ii) a disengage position, in which the air turbine output shaft is not coupled to the at least one engine accessory gearbox mounted accessory, wherein, the lock-up clutch is further configured, in the engage position, to allow the air turbine to respond to changes in the speed of the high pressure spool during both acceleration and deceleration thereof.