ATC separation of IFR flights in class delta airspace

I've been told that towers for most airports in class delta airspace don't have radar, and that tower / ground only controls the movement areas of the airport, and not any actual airspace.

If that's the case, how does ATC provide separation between IFR aircraft on a foggy day where the controllers in the tower cab can't see outside?

 

Pilot reports and time mostly. First of all, the authority to provide IFR Separation will have been delegated to the Tower from the Approach Control or the Center. The authority delegated is usually specific to certain situations. Initial separation between subsequent departures and separating an arrival from a departure is the usual application. There are lots of rules. Some of the basic ones used are a departure must be off before an arrival reports the Final Approach Fix inbound. If subsequent departures will diverge by 45 degrees or more immediately after departure, one minute between them can be used. Separation between subsequent arrivals is usually not delegated to Towers. There are some Non Radar Approach Control Towers. They have full IFR control authority and even handle over flights within the airspace delegated to them. Missoula Montana and Twin Falls Idaho I think are the only two left in the United States.

 

Can you explain this further? I'm not sure I understand how this works. Who would you be talking to and clear you for an approach?

 

Approach Control or the Center clears you for the Approach. They call the Tower and give them an ‘inbound.’ They then switch you to the Tower who tells you to report the FAF. In the meantime, Approach or Center has given the Tower a ‘release’ on a departure. The Tower may launch the departure before the arrival gets to the FAF. If they can’t, they’ll have to wait until after the arrival lands before launching the departure. In the case of subsequent departures, Approach or Center can ‘release’ more than one departure at a time. Tower will launch them one, two, three, maybe more minutes apart depending on type aircraft and routes of flight.

 

Thanks. I guess I thought many Class D non radar control towers worked similar to this? Didn't realize it was something special that only a few places did.

Admittedly, I'm much more familiar with Class D airports that have their own approach control. The only one that operates similar to your description is 75 miles away.

 

Not sure how you'd provide separation when you don't need a transponder to enter delta in the first place.

 

Time, Speed, and Distance.

 

Yeah. Same thing with or without Radar. With Radar ya gots a purty picture of it right thar on yer scope. The trick is knowing what it's going to look like a minute from now. Without it you create the 'picture' in your head.

 

When we talk about Class Ds not having radar, we’re referring to the tower itself. There’s almost always radar coverage (except the few non radar Ds) with the overlying approach/ center. Unless the few times it’s deligated (automatic releases) IFR seperation in the D is provided by them and not tower (local controller).

Also, I’d be willing to bet the majority of Ds have a radar feed now. The problem is there are certified and non certified versions and many restrictions that go with both. In order to find out what your local D has, just call them and they’d be happy to explain. There might be a few Ds (approach / tower combo) that can use their certified tower radar display (CTRD) for sep but the majority can only use them for limited radar functions.

 

Primary radar.

 

All of the control towers the FAA operates now have radar displays, with the exception of two FAA towers with approach controls in the mountain west. The last FAA tower to get one was Lafayette, IN (LAF). There are still several federal contract towers, about 150 in number, that do not have radar displays.

 

FCT's can have Radar displays. I used to work in one. Unless something pretty recent has changed, no FCT has IFR control authority.

 

Yep, I think a bunch of them have radar as well. RYY is FCT and they have a CTRD. Of course many restrictions on what they can use it for though.

 

I do not think Juneau (PAJN) has radar, but has a radar feed.

 

I'm pretty sure KCMA and KOXR have similar set ups. DBrite feeds from Mugu Approach. I believe this is part of the reason they are unable to arrange flight following on the ground, unlike basically all other towered airports in California.

 

No flight following in SE Alaska, look at the map and listen for position reports on 122.9....