February 11, 2007

What exactly does a D-side do?

There are two forms of separation used in air traffic. Radar and Non-radar. While we are almost always using radar data to separate aircraft, we still use forms of separation that do not require radar to get the job done. For instance, any time we have vertical separation (two planes at two different altitudes), that is considered Non-radar separation. The radar comes in when we have planes not yet at different altitudes, but we can assure that by the time they are within 5 miles of each other the vertical separation is there. We can keep planes at the same altitude if we turn one or both of them away from each other and thus use lateral separation.

Whenever I am driving to work, I tend to see things around me as they would relate to how we control airplanes. For example, each lane in of the highway is an altitude. Cars in the right lane are always separated from cars in the middle lane, which are always separated from the cars in the left lane. The key is that each lane is going its own speed. If one car in the right lane slows down, the rest of the cars in the right lane must slow down as well, or, move into the middle lane so they can speed up. In addition, when cars are exiting or entering the highway via the right lane, the cars in the right lane must use their judgment and adjust their speed accordingly to allow the cars to enter or exit without hitting them. In air traffic, this is Radar separation. Determining the sequence and using vectors and speed control to make it work as it happens is the job of the Radar controller, the controller talking to the airplanes.

The other option is to simply switch lanes to the middle lane where you can then go your own pace and there is much less work involved. Cars can get on easily, and you don't have to slow down, speed up, and get stressed out over how to let everyone in. Remember the analogy, changing lanes is like changing altitudes. The key is the look ahead, see the cars approaching on the on-ramp, and switch lanes to make life easier for all. This is the job of the D-side (Radar associate/data controller). D-sides watch the edges of the airspace for aircraft approaching the sector which are in conflict with other planes either already inside the sector or approaching it from other sectors (aircraft which are being handed off from the same sector must be separated when they enter another sector, but very often, aircraft converge into your sector from two or three different sectors). The D-side must then call the other sector on the land line and issue control instructions to that aircraft to change altitudes so they are separated by altitude when they enter the sector.

It is not always that easy, though often times it is. The D-side works with the Radar controller to make a crucial decision as to which of the two aircraft to move. For example, lets assume two aircraft are converging over Ithaca, NY. One is coming from New York Center, the other from Cleveland Center. One aircraft is landing Boston at FL350, the other is flying to Frankfort at FL350. Chances are the overseas flight can't go any higher due to fuel weight, so lets descend the Boston guy. Ideally, we try to keep planes at the correct altitude for direction, so FL330. But if there is a HPN arrival below at Fl330, FL340 may have to be used. This is the basic job function of a D-side.

In the last few years, D-sides have been called upon to make more radar decisions. Perhaps giving the overseas flight a shortcut to the right would cause the flight paths not to cross. Maybe a similar shortcut would make the flight paths cross 40 miles east of where they originally would have crossed in conflict, allowing the radar controller to descend the aircraft arriving HPN first, then incrementally descend the BOS arrival on top of him. Sometimes the best bet is to turn one of the planes 30 degrees off course to fall behind the other aircraft. It is the D-side's job to FIND the conflict and advise the Radar controller. Sometimes the radar controller has a definite plan, and simply informs the D-side what they would like done, other times its a team effort to come up with the best plan.

In addition, the D-side keeps track of all the flight plans on the URET screen. The URET will often alert the D-side of potential conflicts between aircraft with Red boxes. This does not guarantee that the aircraft will be in conflict, nor does a lack of conflict guarantee there won't be a conflict. The key is to understand how each sector works and how that will affect each aircraft. The Frankfort and Boston example is straightforward, but it gets much more complicated when you have to decide between JFK and PIT, PHL and HPN, ALB and SWF, BTV and PSM, MDT and MGW. The key is knowing exactly what each aircraft must do in order to leave your sector correctly, and what the next sector can and won't accept. Aircraft performance and weather also play key rolls in the decision making.

Finally, D-sides handle most, if not all, land line calls to other sectors. These behind-the-scenes calls are to coordinate approval requests, pointouts, and anything else that is out of the ordinary and must be talked over with the other sector.

If you have any questions, send away to deltamike172@hotmail.com

February 3, 2007

Got a map? That may not help....

This post could technically be labeled "Little Airports Part 3", but I chose a unique name instead, as this will act as a transition to another topic.

In my area at Boston Center, we have a joke about the 40N airport. The joke is on Area B (the controllers to our northeast) not knowing what to do with such aircraft. The 40N airport is the Chester County airport in PA, about 30 miles west of Philadelphia (and yes, its completely ironic that the Outer Marker to the ILS Runway 29 approach is named MOSES). Very often, a corporate pilot will be flying along fat, dumb and sufficiently pleased with the ride at FL360 over Albany. Area B flashes the aircraft to us, and we make a phone call to them informing them that they should "treat it like a Philly". They then scramble to dive bomb the aircraft down to FL260 so that we can deliver the aircraft to ZNY over DNY at FL190, just like a Philly. The pilot checks in with us a little perturbed at the fact that we made him spill his coffee just so he could descend sooner than desired.

While 40N is near PHL, why do we have to treat arrivals exactly like a PHL lander? The answer is simple: 40N is within the boundaries of the PHL Approach Control. Every other airport within airspace owned by PHL Approach must be treated in the exact same fashion. While this may seem unfair, and not always the most efficient, it simplifies one aspect of a very complicated system. The only exception to this rule is when the airport inside the approach control is busy enough to justify its own routing for the sake of keeping those aircraft safely away from the aircraft operating at the main airport. Basically, if there are enough planes to get in the way of the main flow, another secondary flow is created. Often, this secondary flow is used for all other airports OTHER THAN the main airport.

Examples: TEB/MMU/CDW are busy enough to require they're own flow apart from EWR. BOS has its own flows into A90 TRACON, and the Satellite airports have another flow which is handed off to a different A90 controller than the BOS arrivals.

But lets get back to the smaller airports. How can you tell which "category" an airport falls into?

Lets take a look at 3 airports in Boston Center, all within 20 miles of each other, but all three are treated completely different because of the airspace structure.

KORE - Orange, MA
KFIT - Fitchburg, MA
KORH - Worcester, MA (pronounced WHUST-uh?)

ORE is a small airport located in an area where ZBW-GDM Sector owns to the surface. This Sector sequences BOS area arrivals, and serves as an approach control for EEN, ORE, and GDM airports. FIT is an airport just inside the A90 TRACON, and thus is treated as a BOS Satellite. ORH is located inside of BDL approach (Y90 TRACON).

Lets see what happens when three aircraft approach from the west of ALB VOR inbound to these three airports.

The FIT arrival is routed via ALB..GDM.V431.LOBBY..FIT and issued a restriction to cross 40 west of ALB at FL290, descended to FL230 about 40 miles east of ALB, and then descended to cross BRONC at 6000, unless Runway 14 is requested, in which case, the arrival is descended lower for the approach.

The ORE arrival is routed via ALB..EEN/GDM..ORE (if not just direct ORE) and descended to FL230 about 30 west of ALB (vicinity of SWEDE), then descended to 11000 40 east of ALB, and then descended for approach by the GDM sector. This flow is meant to be below the BOS Satellite arrivals, avoiding the high altitude sector that feeds the GDM Sector.

The ORH arrival is routed south of ALB via RKA.SWEDE1.ORH. This may be the most obvious of the three routings, as ORH is listed on the SWEDE1 chart. These arrivals cross SWEDE anywhere between FL230 and FL180, then descended to 11000 and handed off to Y90 TRACON about 30 miles southeast of ALB.

What was the question again? Here's the answer:
If you're not sure what route to file into a small airport, take a look at the approach charts. Which facility has its frequencies listed on the chart? That main facility is your clue to how "you'll be treated" and how to file your flight plan. That's how controllers like me figure out where you're going!