Tower En Route Control
So say you want to do a quick IFR flight from one airport in a “terminal” environment to another in a “terminal” environment (basically two airports close together covered by an approach controller). This is when you could request to use TEC, or tower en route control. i.e. Flying from KSRQ to KPIE and both airports are covered by Tampa approach.
The main benefit to a TEC clearance is you can call ground last minute when you are taxiing out (or clearance) and ask for “IFR Tower En Route” between two airports, kind of like a “pop-up ifr clearance” (we’ll talk more about that later). Ultimately it may just save you a little time in having to file an entire IFR flight plan if you are already on the taxi out and realize the weather is getting lower than forecast, and you’d like to go IFR instead of VFR (or at least have the option to get a little closer to the clouds).
While it is not commonly used, it is a tool in your back pocket as an instrument-rated pilot. You can also file a regular IFR flight plan and place in the remarks section “TEC” or “Tower En Route”. Meaning you’d like to just stay on with approach controllers rather than going out in the greater NAS and talking with Center controllers.
TEC is primarily for short flights (2 hours or less) and for low (10,000′ or less) altitude flights (often times you will use the preferred routes between two airports that are published in the chart supplement).