On Sep 19, 7:43 am, John wrote:
On Sep 17, 5:10 pm, Andrew Gideon wrote:

I vaguely recall someone mentioning to me once that there was an AD
regarding cigarette lighters in Cessna 172s of some vintage. But I've
searched around trying to find this (including at the FAA web site), and
have failed.

Anyone have pointers (or is this perhaps an "urban myth")?

Thanks...

Andrew

Here is the AD number and list of applicable aircraft from 120 to
T210. I have found I had to perform the service bulletin referenced
in the AD on a CE 177RG even though the AD did not apply. A resistor
in the cigar lighter system was consistently burning up.

The original problem was that the lighter socket went
straight to the bus without any circuit protection whatever, and a
short in that system caused electrical fires. I think the resistor was
in the 177 and some other later Cessnas to drop the 24-volt supply to
12 volts for the standard cigar lighter, and that resistor, carrying
so much current, got pretty hot. Any wires that a later technician
tied up against it would get burned, too.
We have 1-amp fuses in the lighter socket line so that
accessories such as GPS can be plugged into it. We don't allow smoking
in our airplanes. Smoking ruins gyros in short order, too.

Dan