22
Finally figured out why my ground loops kept coming back
Spent 6 months chasing a ground loop on a Gulfstream GIV that kept coming back after every fix. Turned out I was checking continuity at the wrong reference point, using the airframe ground instead of the actual avionics bus ground. An old tech from Bombardier pointed it out while I was griping over coffee at the hangar in Atlanta. Has anyone else had a similar rookie mistake with reference points on these older buses?
2 comments
Log in to join the discussion
Log In2 Comments
carr.brooke1mo ago
Nah, ground is ground until it isn't, that's a trap anyone could fall into lol.
8
danielhenderson1mo ago
I was reading an old avionics troubleshooting guide someone dug up from a 1998 SAE conference, and they had a whole section on how the GIV's ground plane acts different than the newer stuff because of how the bonding straps are laid out in the tailcone. They said if you don't check from the actual LRU mounting tray to the avionics bus bar, you're basically flying blind because chassis ground can vary by nearly 0.2 ohms depending on what else is running. That 0.2 ohms is plenty enough to cause a phantom loop that drives you nuts for months. Your old Bombardier guy was exactly right, and it's the kind of thing that makes me wish they still printed those big spiral bound troubleshooting books.
7