Pro tip: Check the ground before you blame the box

I was troubleshooting a comms issue on a King Air last week, the VHF radio kept cutting out. I spent a good hour chasing it through the system, checking connections and power at the radio itself. Everything looked fine at the unit, so I was about to call it a bad LRU and start the paperwork. My lead, who's been doing this since the 90s, just looked at me and said, 'Did you actually check the antenna ground?' I hadn't. Sure enough, the ground strap from the antenna base to the airframe was corroded and barely making contact. Cleaned it up, problem gone. I learned that the issue isn't always at the expensive black box you're staring at. It's often the simple, boring stuff you skip because it seems too obvious. Anyone have a good method for checking those ground paths quickly without pulling half the interior panels?

3 comments

3 Comments

ninab9521d ago

On a 172 I was working on the VOR receiver kept losing its lock in flight. I ran through the wiring diagram twice, checked the antenna cable connector, even swapped a card. Then I remembered a trick from my A&P instructor. I took my multimeter and checked resistance from the antenna base mounting screw to a clean spot on the firewall. Got a reading of about 15 ohms, way too high. The ground bond between the antenna mount and the skin was gunked up with old corrosion. Wire brushed both surfaces and put some conductive compound on, lock came right back. It's a five minute check that can save you a day of head scratching.

spencer1992mo ago

Heard a guy say a cheap multimeter on continuity check is your best friend for that.

evannelson2mo ago

Oh man, that's a classic. @spencer199 is totally right, a basic multimeter on beep mode is the go-to. I got burned once on a nav light that kept popping breakers. I was ready to replace the whole harness. My buddy just touched one probe to the light housing and the other to a clean bolt, got no beep. The ground path was shot right at the base. Saved me a ton of time and a stupid mistake. Now I always check continuity from the component ground to the airframe before I even open the book.