Interchangeability of Components
Swapping components between ETOPS aircrafts similar primary systems for trouble-shooting purposes (e.g. installing #1 GCU in the #2 GCU location to ascertain if a problem is with the #2 GCU or further up the system) should be done using extreme caution. Every precaution should be taken to assure that damage to the system not in question, will not be affected. In those cases where similar components are swapped, positive verification of system integrity per Part 12, RESOLUTION OF AIRCRAFT DISCREPANCIES, is required for both systems.