A robotic arm is provided, for example for inspecting a rotary machine such as a gas turbine engine. The arm has a plurality of groups of links having articulations therebetween for movement in a first plane, the groups having articulations with respect to each other for movement in a second orthogonal plane. Thus the arm can move around objects such as aerofoils in the engine, and also move up or down to remain close to the rotary surface of the machine.