A thrust reverser actuation system, comprising: a first cowl actuation system for translating a first cowl of a thrust reverser; a second, separate cowl actuation system for translating a second cowl of the thrust reverser; a motor configured to drive the first and second cowl actuation systems (62A,62B), wherein the first and second cowl actuation systems (62A,62B) each comprise a separate primary drive shaft (30A,30B) operatively connected to the motor, wherein each primary drive shaft (30A,30B) provides the main drive for the respective first or second cowl actuation system (62A,62B); a device operatively connected between the first cowl actuation system and the second cowl actuation system, and configured to transmit drive from one of the first and second cowl actuation systems (62A,62B) to the other of the first and second cowl actuation systems (62A,62B); characterised by the device comprising a lost motion device configured to drive the other of the first and second cowl actuation systems (62A,62B) upon failure of the other of the first and second cowl actuation systems (62A,62B); and in that the device comprises a first shaft operatively connected to the first cowl actuation system, a second shaft operatively connected to the second cowl actuation system, and one or more intermediate components configured to transmit drive between the first shaft and the second shaft, wherein, upon failure of the first cowl actuation system or the second cowl actuation system, one of the first shaft and the second shaft will no longer be under the control of the motor and will be free to rotate without restriction. a first cowl actuation system for translating a first cowl of a thrust reverser; a second, separate cowl actuation system for translating a second cowl of the thrust reverser; a motor configured to drive the first and second cowl actuation systems (62A,62B), wherein the first and second cowl actuation systems (62A,62B) each comprise a separate primary drive shaft (30A,30B) operatively connected to the motor, wherein each primary drive shaft (30A,30B) provides the main drive for the respective first or second cowl actuation system (62A,62B); a device operatively connected between the first cowl actuation system and the second cowl actuation system, and configured to transmit drive from one of the first and second cowl actuation systems (62A,62B) to the other of the first and second cowl actuation systems (62A,62B); characterised by the device comprising a lost motion device configured to drive the other of the first and second cowl actuation systems (62A,62B) upon failure of the other of the first and second cowl actuation systems (62A,62B); and in that the device comprises a first shaft operatively connected to the first cowl actuation system, a second shaft operatively connected to the second cowl actuation system, and one or more intermediate components configured to transmit drive between the first shaft and the second shaft, wherein, upon failure of the first cowl actuation system or the second cowl actuation system, one of the first shaft and the second shaft will no longer be under the control of the motor and will be free to rotate without restriction.