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MAINTENANCE TIP
A Seemingly Simple Squawk
A trip down the troubleshooting trail
by Dean Benedict
PHOTO CREDIT: ROB TURCHICK/YIPDOG STUDIOS
Acustomer called to say his R/H generator went offline mid-flight. He happened to have an F90, but this squawk could happen with any King Air. For troubleshooting purposes, I suggested he swap the generator control units to see if the problem went to the other side, and it did. I had an exchange GCU drop-shipped to him and it was installed on the right side, putting the GCU that came off the left side back in its original position.
Everything worked fine on the ground, but going through 12,000 feet on the next flight the right generator
dropped offline again. He flew to my shop so I could take a further look. We took the usual troubleshooting steps such as ringing out all the wiring between the GCU and the generator to confirm continuity. We found no obvious smoking gun, but we tweaked a few things, installed another exchange GCU and it ran great on the ground.
Frustration
On the next flight, going through 12,000 feet, the right generator dropped offline yet again. By then I was frustrated. As it turned out, this was only the beginning of a long and difficult journey that came to be known around my shop as “The Great GCU Saga.” I will spare you some of the excruciating details and most of the expletives that proliferated throughout this aggravating experience.
12 • KING AIR MAGAZINE
FEBRUARY 2025