ATM Modernization, Commercial

Airframer Advances Surveillance Techniques

By Douglas W. Nelms | October 1, 2007
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While ADS-B is the latest catch phrase in air-traffic management, it is not all that new. Many airliners flying throughout Europe already have some Automatic Dependent Surveillance-Broadcast (ADS-B) capabilities, and official certification of ADS-B "Out" capability either later this year or in early 2008 will allow its limited use.

A major benefit is that certification will facilitate full adoption of Airbus’s Airborne Traffic Situational Awareness (ATSAW) program designed to improve aircraft surveillance and navigation standards and enhance flight crews’ knowledge of the surrounding traffic situation.

Eurocontrol has stated it will use ADS-B as one of the primary pillars for future air-traffic management, using 1090 MHz Extended Squitters, or data signals, as the preferred communications link. The agency’s CASCADE (Co-operative ATS through Surveillance and Communication Applications Deployed in ECAC) program will lead and implement the use of ADS-B.

The necessary avionics, primarily the 1090 MHz Mode S transponder, Traffic alert Collision Avoidance System (TCAS) and appropriate software, will be installed in all Airbus aircraft and receive European certification in 2009, said Laurent Vidal, Airbus manager of surveillance systems.

Airbus has been pushing for early implementation of ADS-B Out using Mode S Extended Squitters for improved cockpit separation control, primarily using avionics already available on commercial airlines and approved under the DO-260 standard.

Final certification of ADS-B Out will be the enabler to ATSAW and future ADS-B "In" applications, leading to new separation standards for commercial airliners operating on oceanic routes, the airframer said.

Every second, an ADS-B transceiver sends out its identification, position, altitude and other data — the function known as ADS-B Out. Data uplinked from air-traffic control centers, including weather forecasts and traffic advisories, as well as from other aircraft, is known as ADS-B In.

ATSAW is designed to validate the ability of pilots to receive information on all surrounding aircraft, as well as ground vehicles on the airport surface, providing the position, direction, relative altitude, ground speed and vertical speed tendency of other aircraft.

The program is described as the first step of the Airborne Separation Assistance System (ASAS), the surveillance component of Communication, Navigation and Surveillance, Air-Traffic Management (CNS/ATM) improvements being developed with ADS-B.

Airbus also is working with Eurocontrol on the ATSAW part of the CASCADE program that ultimately will implement ADS-B in Europe. This is the next layer of CNS and will implement Controller Pilot Data Link Communications (CPDLC) to provide data communications between pilots and air-traffic controllers.

Eurocontrol is working with organizations such as DSNA, France’s air navigation services directorate, and engineering firm Sofreavia, on CASCADE. Within CASCADE is CRISTAL, or Co-operative Validation of Surveillance Techniques and Applications, which is a collection of ground and airborne surveillance validation projects. The Airbus program is CRISTAL ATSAW, with the main objective to facilitate the smooth integration of ATSAW into air traffic management practices.

Three applications

Airbus is currently using ATSAW to test and validate three applications of what eventually will be a worldwide ADS-B system — In-Trail Procedure (ITP) in oceanic and other remote airspace; Enhanced Visual Separation on Approach (VSA) and Enhanced Traffic Situational Awareness on the airport surface. These applications were chosen for economic and safety reasons, to be implemented in two steps. The first step will be combined ITP and visual separation approaches; the second will be enhanced traffic situational awareness on the airport surface.

Enhanced situational awareness will permit pilots to reduce the separation between aircraft in oceanic airspace from 10 minutes, or roughly 80 nautical miles, to 20 nautical miles, as well as changing altitudes more frequently in order to optimize fuel burn and avoid turbulence. Currently, 30 percent of requests for altitude change are denied. With ATSAW, that number should be reduced by half, saving millions in fuel costs, Vidal said.

While improved ITP is designed to reduce oceanic and remote area separation, improvement in visual separation on approach is designed to improve the procedure for flight crews to acquire and maintain visual contact with the preceding aircraft, enable the flight crews to maintain a more precise distance from the preceding aircraft and extend the meteorological conditions under which visual approaches may be safely performed. This, in turn, will lead to increased fuel savings, decreased noise levels and a decrease in missed approaches, Airbus said.

The system also will provide pilots with wake vortex information. "Ultimately we’ll see spacing that is governed more by wake vortex constraints," observed a spokesperson for the Air Transport Association, representing the airline industry.

"The technology will be good enough to put airplanes nose to tail, (although) the physics of it will dictate that there is greater spacing than that."

ATSAW is simply the first step in improving separation surveillance, Vidal said. The information, experience and confidence gained will allow future ASAS applications that will enable flight crews "to achieve and maintain automatically a given spacing with designated aircraft as specified in new ATC instructions."

In turn, this spacing is foreseen as a solution to avoid use of radar vectoring techniques, thus enhancing traffic regularity during the approach to dense airports.

Vidal also emphasized ATSAW does not transfer responsibilities between pilot and air traffic controller. For changes in altitude, ATSAW will allow the pilot to determine the safety of climbing or descending to a more optimum flight level, then request that altitude from the controller with a better chance of receiving approval.

Although ADS-B Out has not yet been certified, Airbus is already testing the full use of ADS-B for surveillance and aircraft spacing, which will require both ADS-B Out and In capabilities.

For ADS-B Out, Airbus said there is no need to retrofit current transponders and that certification and operations can be conducted using existing equipment. Most transponders currently installed on aircraft and having the extended squitter capabilities are compatible with DO-260, Airbus said.

However, DO-260A has superseded DO-260 and is the current requirement for 1090 MHz Extended Squitter Minimum Operational Performance Standards (MOPS). DO-260A will require that transponders be upgraded to the latest standard for integrated surveillance systems on the Airbus 380 and Boeing 787, and that they are compliant at entry into service. All new Airbus aircraft are being equipped with avionics to meet DO-260A standards, Vidal said.

"Because of Airbus’ efforts, over half of the flights operating in Europe already have ADS-B Out," said Arnold Oldach, principal systems marketing manager for Rockwell Collins. "What really enabled this was the European mandate for elementary surveillance (ELS) and enhanced surveillance (EHS). When we had to modify our transponders to meet ELS and EHS, all the manufacturers implemented DO-260 Extended Squitters in their transponders. That was at the behest of Airbus. They have been at the leadership forefront in developing the surveillance system and getting it out there for the industry."

Onboard Surveillance Systems

On-board, integrated surveillance systems, combining TCAS, transponder, weather radar and Terrain Avoidance Warning System (TAWS), are being developed by Rockwell Collins for the B787 and by Honeywell for the A380.

Airbus calls its integrated system the AESS, or Aircraft Environmental Surveillance System, developed in conjunction with Honeywell. The Rockwell Collins system is called simply the Integrated Surveillance System (ISS). Aviation Communications & Surveillance Systems (ACSS) offers the "SafeRoute" system, a software program (Avionics, June 2007, p. 32).

Rockwell Collins and Honeywell will be competing for the AESS position on the Airbus 350XWB.

Rockwell Collins has introduced the CISS-2100 Configurable Integrated Surveillance System, expected to be certified next year on the Dreamliner. A similar integrated system from Rockwell Collins is the TSS-4100 Traffic Surveillance System being developed primarily for corporate and regional jet aircraft. This will have the same level of ATSAW traffic computer capability as the CISS-2100, said Arnold Oldach, principal systems marketing manager for Rockwell Collins.

ACSS announced at the Paris Air Show in June that it had received Supplemental Type Certification (STC) for the SafeRoute system on Boeing 757s, clearing the way for installation on UPS freighters following the issuance of TSO-C166, the Technical Standard Order for ADS-B.

The company also announced the signing of an agreement with Airbus to study the certification of T3CAS, an integrated TCAS, TAWS and Mode S transponder system, for the A320 and A330/A340 families. T3CAS is a single line-replaceable unit with lower cost, less weight and volume and improved power efficiency, said Chuck Manberg, ACSS technical lead for ADS-B.

ADS-B Presents Procedural, Display Challenges

In the United States, the FAA is looking at Automatic Dependent Surveillance-Broadcast (ADS-B) as a way to replace its secondary surveillance radar system as well as to enhance airspace surveillance capability. In Europe, the airline industry believes there should be greater responsibility in the cockpit based on the pilots having greatly enhanced situational awareness.

While Eurocontrol expects initial operation of ADS-B in 2011, the U.S. time frame for system operations is 2018-2020. FAA’s plan to publish a Notice of Proposed Rulemaking this fall will be the first step toward nationwide implementation of ADS-B.

The Air Line Pilots Association (ALPA) contends the full benefits of ADS-B will not be realized by air transport pilots until the tools provided by ADS-B In are added, and "encourages the FAA and industry to work toward moving the ADS-B In time line to a more near-term reality," said Capt. Brian Townsend, chairman of ALPA’s National Airspace System Modernization Committee.

"The combination of ADS-B In and Out will enable both the pilot in the air and the controller on the ground to see the same situational ‘picture’ and make collaborative decisions together on the most optimum flight profile," Townsend said. "ALPA believes this is vital for enhancing the safety of the air transportation system and for increasing capacity in all operational environments — oceanic, en route and terminal."

One of the challenges facing avionics developers is simply how pilots are going to receive the information made available by ADS-B.

"What the pilots see in the cockpit and how they use it are certainly issues that have to be addressed," said a spokesman for the Air Transport Association (ATA). "We’re really a long way off from talking about what the cockpit of the future will look like. We know the kind of things that have to be there. But the trade-offs are that there is a lot of information you can put in front of the pilot, and at some point the concern is that you can put too much there so that it becomes a distraction."

Older aircraft with smaller display screens have trouble displaying traffic, said Arnold Oldach, marketing manager for Rockwell Collins.

"For example, the 757s and 767s have navigation displays that are generally agreed to be not large enough to adequately display sufficient ADS-B targets," Oldach said.

"These are representative of the display sizes on aircraft of their generation and are fairly small so you can’t really put traffic on them. Even the new 737s, which are larger, are a struggle because the inclusion of ADS-B targets requires additional processing capability and we don’t yet fully understand how much processing will be required."

Through its "SafeRoute" application, Aviation Communications & Surveillance Systems said data will be displayed through the Cockpit Display of Traffic Information hosted in Boeing’s Class 3 Electronic Flight Bag, manufactured by Astronautics Corp. of America and certified to DO-178B, Level C software criticality.

"Today we are looking at the basic displays we have, and we’re adding electronic flight bags, but even having that additional display in the cockpit can present challenges," the ATA spokesman said. "We’re talking about using it to taxi around on the airport surface, putting moving maps on there and things like that.

"It helps you know your position on the airfield and helps you navigate, but it also requires a pilot to have a heads-down stance in the cockpit and not be looking out the window," he added. "So you know exactly where you are, but your eyes are down instead of up…. Those are the things that have to be addressed for something as simple as a moving map display."

Future surveillance applications may involve a head-up display that provides the right information and gives the pilot situational awareness through a moving map that provides the position of the aircraft on the airport as well as other aircraft and ground vehicles. — Douglas Nelms

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