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Tuesday, June 1, 2010

ADS-B: Thing of Beauty

By Pat Gray

Automatic dependent surveillance-broadcast (ADS-B) in the Gulf of Mexico is: “A thing of beauty.” Those were the actual words of the controller during the interview at Houston’s ARTCC radar control room. Gerard Quiroz, a front line manager and Kim Pettis, Houston Center, National Air Traffic Controllers Association (NATCA) ADS-B representative, were in agreement. They gave a frank and to-the-point assessment on just what the controllers have experienced to date while operating the scopes and talking to the pilots flying the newly implemented ADS-B system in the Gulf of Mexico.

We started out by looking at controller training—actually, there is no formal national training program for ADS-B. It turns out that a seamless transition exists between the NAS radars and ADS-B. The visual display on the scopes is almost identical to current radar displays throughout the NAS, so the training consisted primarily of verbal briefings and a two-hour simulation to familiarize the controllers with airspace and procedural changes.

It is important to realize that the Gulf of Mexico encompasses a vast amount of airspace—in fact, it is almost 50 percent of Houston ARTCC’s total airspace. To date, at least 90 Houston controllers have worked ADS-B equipped helicopters. There is a unanimous feeling among the controllers that ADS-B will be a tremendous step forward by the FAA in the ATC field. One controller commented that, “we can see traffic that we have never seen before” and when you are a controller, that is the heart and soul of the job—having a visual target on the screen.

To give some history, under the non-radar procedures, which are still being used in the Gulf IFR helicopter airspace, aircraft are routed along GPS geographical waypoints that FAA developed, located every 20 minutes of latitude and 20 minutes of longitude. This GPS grid system serves as the route structure for IFR operations between the on-shore bases to the offshore platforms. The spacing between the waypoints also accommodates the non-radar lateral and longitudinal separation standards within the airspace. In this non-radar environment, separation is verified via VHF voice communication between controller and pilot.

Because of line of sight limitations with VHF, areas of limited communication exist, thereby increasing controller workload. This is especially true if position reporting and ATC clearances are being relayed through an operator’s dispatch center. The non-radar procedures reduce the route flexibility for both controller and pilot. These flights are required to file and fly the waypoint grid system on a north-south, east-west or diagonal course. This results in a very structured flight profile, adding flight time and delay.

On the other hand, ADS-B flights are allowed to operate directly at the boundary of Center and Approach Control airspace and then directly to the waypoint that serves the destination. This is allowable because the controller maintains surveillance on the ADS-B equipped helicopter. This also reduces the workload for both controller and pilot because position reporting is no longer required.

By adding surveillance to the Gulf airspace, some additional complexity is added to the controllers job due to having a combination of ADS-B equipped IFR helicopters and those not equipped. Sooner or later, within this mix, some traffic will cross or request a climb and the controller will have to provide separation. This not only slows down the operation, but also creates a three-dimensional math problem for the controller. Think of a stack of eight aircraft holding over a fix. Seven of the aircraft are non-radar and the third from the bottom (in radar contact) has to descend through the altitudes of those underneath. The controller can get them down but, because of the mix, has to use a greater separation standard for some of the aircraft during the process.

With implementation of NextGen products like ADS-B, FAA—which has mandated ADS-B on all aircraft by 2020—will change it philosophy of “first come, first served” to “best equipped, best served.”

When Houston Center turned on ADS-B in December 2009, there were seven helicopters equipped to utilize the system. To date, there are 37 equipped with more coming online daily.

Houston Center is pro-active in accommodating this increase. Its controllers are working hard because they want this system to succeed. They say cooperation by pilots, the oil industry, helicopter companies and contractors is at an all time level of commitment.

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