For two reasons: (1) it costs less to perform the biannual
inspection, and (2) you aren't broadcasting your tail number to the
Feds. Of course, you'll only get a 10 year life out of it...

-John

On Dec 8, 2:54 pm, Andy wrote:
Why would anyone buy a mode C transponder when for only a little more
one can buy a mode S unit?

Andy