An actuator (214; 314; 514; 614) operable to drive a thrust reverser (2'; 102; 402) in a gas turbine engine, the thrust reverser (2'; 102; 402) comprising a linear translating cowl structure contained within a nacelle surrounding the gas turbine engine, the linear translating cowl structure comprising a first sleeve (4; 104; 404) and a second sleeve (6; 106; 406); wherein the actuator (214; 314; 514; 614) comprises a first actuating member (242; 342; 542; 642) moveable so as to translate the first sleeve (4; 104; 404), and a second actuating member (244; 344; 544; 644) moveable so as to translate the second sleeve (6; 106; 406), between positions corresponding to the thrust reverser (2'; 102; 402) being open or closed; the actuator (214; 314; 514; 614) further comprising an interlock arrangement (246; 346; 546; 646) operable in a locked mode in which the first actuating member (242; 342; 542; 642) and second actuating member (244; 344; 544; 644) are locked so as to move together and in an unlocked mode in which at least one of the first actuating member (242; 342; 542; 642) and second actuator member (244; 344; 544; 644) is free to move independently of the other; wherein the first actuating member (242; 342; 542; 642) and second actuating member (244; 344; 544; 644) are further arranged such that operation of the actuator (214; 314; 514; 614) to open or close the thrust reverser (2'; 102; 402) comprises: a first mode wherein the interlock arrangement (246; 346; 546; 646) is in the locked mode and the first (242; 342; 542; 642) and second actuating members (244; 344; 544; 644) are driven to move together along a first predetermined distance; and a second mode wherein the interlock arrangement (246; 346; 546; 646) is in the unlocked mode and either the first actuating member (242; 342; 542; 642) or the second actuating member (244; 344; 544; 644) is driven to move along a second predetermined distance independently of the other actuating member; wherein the position of the interlock arrangement (246; 346; 546; 646) determines the first and/or second predetermined distances; characterized in that the interlock arrangement (246; 346; 546; 646) comprises one or more moveable segments (246; 346; 546; 646) which act between the first actuating member (242; 342; 542; 642) and the second actuating member (244; 344; 544; 644) so as to mechanically couple the first (242; 342; 542; 642) and second actuating members (244; 344; 544; 644) together. a first mode wherein the interlock arrangement (246; 346; 546; 646) is in the locked mode and the first (242; 342; 542; 642) and second actuating members (244; 344; 544; 644) are driven to move together along a first predetermined distance; and a second mode wherein the interlock arrangement (246; 346; 546; 646) is in the unlocked mode and either the first actuating member (242; 342; 542; 642) or the second actuating member (244; 344; 544; 644) is driven to move along a second predetermined distance independently of the other actuating member; wherein the position of the interlock arrangement (246; 346; 546; 646) determines the first and/or second predetermined distances; characterized in that the interlock arrangement (246; 346; 546; 646) comprises one or more moveable segments (246; 346; 546; 646) which act between the first actuating member (242; 342; 542; 642) and the second actuating member (244; 344; 544; 644) so as to mechanically couple the first (242; 342; 542; 642) and second actuating members (244; 344; 544; 644) together.