Figured I'd jump in and throw another topic up for discussion here. The concept of how to solicit and apply visual separation. Unfortunately, throughout the process of flying under the control of a number of facilities as well as training controllers within my own, I've found that visual separation is a often misunderstood and misapplied concept. Key examples of this include, but are not limited to:
- Attempting to apply visual separation in the flight levels
First, in order to establish some definitions, let's look at 7110.65 7-2-1, which states:
Visual separation may be used up to but not including FL 180
Yep. Can't use it in Class A airspace. Have to have lateral, vertical, and/or wake turbulence separation. no exceptions.
About the only exception to applying visual separation in the flight levels is to climb or descend through traffic below Class A airspace. For example, if you have a climbing aircraft with traffic above him at 17,000, an aircraft is allowed to climb into Class A airspace after visually separating from an aircraft no higher than 17,000 feet MSL. The reasoning is the instant before the aircraft breaks the plane into Class A airspace visual is no longer being applied and “separation after” will exist. An aircraft at FL 180 is also allowed to transition out of Class A airspace using visual separation if the visual maneuver will be a descent through the altitude of another aircraft at or below 17,000 feet MSL. The reasoning is that separation exists before the aircraft descends and visual is not applied until the descent starts. At that instant, the aircraft will also be out of Class A airspace.
It's important to note that if altimeters are below 29.92, meaning FL 180 is not an assignable altitude and FL 190 or above is usable, any visual separation maneuver out of FL 190 or above would begin in Class A airspace. This is not an allowable application, therefore nullifying transition out of Class A airspace. The reasoning is that FL 180 is still a discernible altitude just not an assignable altitude.
- Attempting to apply visual separation between aircraft between which a loss of radar separation has already occured
- Not establishing a form of prescribed separation both before and after the application of visual
These two basically go hand in hand. Visual separation is meant to be used as a tool to expedite traffic which is already separated by another form of legal separation. If you're using it to try and save a deal, tough luck:
Visual separation may be applied when other approved separation is assured before and after the application of visual separation. To ensure that other separation will exist, consider aircraft performance, wake turbulence, closure rate, routes of flight, known weather conditions, and aircraft position. Weather conditions must allow the aircraft to remain within sight until other separation exists. Visual separation is not authorized when the lead aircraft is a super.
In a nutshell, when using visual separation to climb or descend through traffic, the aircraft must be positively separated (typically assigned vertically separated altitudes) prior to the use of visual separation. Separation after is then ensured by the assignment of altitudes to both aircraft that will ensure vertical separation, or by headings/courses that will diverge to minimum lateral separation.
You can also use it to waive wake turbulence separation when operating underneath or behind large/heavy aircraft (NOT Supers). When applying this on successive arrivals to the same runway, this effectively means that your "separation after" the application of visual is runway separation appropriate to the categories of aircraft involved.
Either way, it's a tool, not a crutch. Use it wisely and proactively. It goes hand in hand with ensuring positive separation of your traffic!
- Advising VFR aircraft to maintain visual separation with other aircraft (not used outside of Class B/C and for a very specific use case at the tower level)
Remember that within Class B airspace, VFR aircraft are radar separated from all IFR and VFR aircraft by either target resolution/500 ft vertical (from aircraft weighing 19,000lb or less) or by 1.5 miles/500 feet vertical (from turbojet aircraft and aircraft weighing >19,000lb). In Class C airspace, VFR aircraft are radar separated from IFR aircraft only by target resolution/500 ft vertical.
You can use visual separation to your advantage in these airspace strata to expedite VFR traffic movement, but all too often, I hear it being applied in the pattern at Class D towers. The only time visual separation would apply within Class D airspace would be in a case when you're faced with a Small weight class aircraft (< 41,000lb) performing a touch/go or stop/go after a departing Small+, Large, or Heavy aircraft.
The reason for the use of visual separation in this case is that once the landing portion of the touch/go or stop/go is complete, the Small aircraft effectively transitions from being an arrival to being an intersection departure. We're required to have 3 minutes of wake turbulence separation for a Smal intersection departure following a Small+ or greater full length departure. Advising the Small aircraft to maintain visual separation with the departing larger aircraft is the "out" in this case. The phraseology for this is as follows:
N12345, report the departing B737 in sight.
Departing B737 in sight, N12345.
N12345, maintain visual separation with the departing B737, caution wake turbulence, runway 1, cleared (touch and go/stop and go/for the option)
We see so little pattern work on VATSIM that this one probably won't come up very often, but it's pretty much the only time you'd hear a controller at a Class D tower issue visual separation, which is why I bring it up.
Hopefully the explanations above give you guys some insight into how and when visual separation can be properly used to help run your traffic flow more efficiently while still maintaining legal separation throughout the process. There are a few other cases where visual separation can be used (successive departures being the most notable) that some of the other r/w guys who work in towers can probably shed some light upon, but these are the ones that I wanted to hit on based on my time spent flying, controlling, and training on the network.
