Abstract: An aircraft gas turbine engine has first and second electrical harnesses formed from respective first and second flexible printed circuit boards which each provides a plurality of spaced conductive tracks. The conductive tracks carry signal types which either (i) provide engine control and can cause hazardous engine conditions in the event of their failure, (ii) detect or prevent hazardous conditions of the engine, or (iii) are not of type (i) and/or of type (ii). The first flexible printed circuit board provides all the conductive tracks which carry signals of type (i) or the first flexible printed circuit board provides all the conductive tracks which carry signals of type (ii). The second flexible printed circuit board provides all the remaining conductive tracks. The first electrical harness is fire-resistant for a period of five minutes without any exposure of its conductive tracks so that the conductive tracks can carry their signals.