Scalar Chain refers to a pre-defined, formal path of authority and communication in the order of highest to the lowest. For example- if A is the CEO of an organisation and he has two paths of authorities under him. One, A-B-C and the other A-D-E. Everybody in the organisation follows this chain of authority for communication. For example, If C wants to contact with E then he will have to follow this formal path, as C → B → A → D → E. That is, C has to first contact the higher authorities (C → B → A) over him who then transverse the communication to E (A → D → E).
However, in case of emergency C may directly contact E through ‘Gang Plank’. Gang plank is a shorter emergency route through which the workers lower in the authority chain can directly contact the persons of higher authority or those working in other scalar chains.