IEC 61821:2011 applies to the maintenance of AGL constant current series circuits. This International Standard: - covers constant current series circuits for AGL installed at aerodromes and heliports; - concentrates on providing the safety requirements for the maintenance of an AGL constant current series circuit. It is recognized that AGL constant current series circuits of different design characteristics and parameters are in existence; - is mainly concerned with safety to persons by specifying the rules and fundamental principles for the maintenance of AGL constant current series circuits; - is not intended to apply to AGL primary series circuits supplied directly from a mains constant voltage source; - is not intended to be used for public street lighting, roadway lighting or any other installation requiring the use of constant current series circuits. This second edition cancels and replaces the first edition published in 2002. It is a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) addition of references to normative references; b) addition of notes in Clauses 5, 6 and 7; c) modification of pre-work procedures in item e) of 7.2.2.