an igniter for a gas turbine engine . an igniter generates a plasma , or spark , somewhat similar to an automotive spark plug . in the invention , an auxiliary electrode is provided , which is embedded in and covered by a solid insulator . during initial phases of operation , no part of the plasma generated contacts the auxiliary electrode . however , eventually , the covering insulation is eroded by the plasma , and the auxiliary electrode becomes exposed and available as a return path for the plasma . the igniter is constructed so that , when this erosion occurs , the lifetime of the igniter is near its end . detection of this erosion , as by detecting the new current in the auxiliary ground electrode , indicates the approaching end - of - lifetime .