Be my guess that departing from the airport where the Approach Control is
located internal operating procedures contain provisions for a "silent
release' of departing IFR aircraft. If you are at an airport that is
colocated with approach control an individual release is required.
Al

"Dave Butler" wrote in message
news:1127496435.982217@sj-nntpcache-3...
John Clonts wrote:

snip
Later I thought that maybe the tower didn't realize I was IFR when he
cleared me for takeoff, and that fouled something up with departure.
snip

This is an interesting thread. I'm based at a class C, RDU,
Raleigh-Durham, NC, and I've never had that happen, and I've never
informed tower that I was IFR. Never heard anyone else do it either.