Incremental improvement of the US airspace system is achieving results, but pressure is building for a more sweeping modernisation

If North American air traffic managers have learned anything over the past 12 months, it is that any future airspace system must be flexible enough to cope with the unexpected. While the overall drop in traffic from the year before was not unexpected given the events of 11 September, the shifting mix of traffic has come as a surprise and is already influencing the design of the future US air traffic management (ATM) system.

The increased number of regional jet movements, the shift of flights from hubs to secondary airports and the increased business jet activity over the past year have combined to ensure that North American airspace has been busier than the overall decline in traffic would suggest. With regional jets expected to make up one third of the US airline fleet by 2006;fractional-ownership companies already operating hundreds of business jets; and explosive growth predicted in the long term for air-taxi operations using small jets; any future ATM system needs to be flexible and responsive.

In 2001, the US Federal Aviation Administration put in place the Operational Evolution Plan (OEP), a 10-year package of improvements designed to produce measurable benefits in capacity and efficiency. The initial 10-year plan supported a 30% capacity increase. This has since been revised upwards and will again be updated after the FAA's forecast conference early next year.

Key technologies

Included within the OEP is the phased deployment of key new technologies such as free flight, automatic dependent surveillance-broadcast (ADS-B) and controller-pilot datalink communications. Meeting the capacity and efficiency goals depends on users equipping to take advantage of these new technologies. But some of the capacity increases come through airspace redesign. The FAA says 15 choke points were changed last year, resulting in a 15% reduction in delays in key corridors in the north-east USA and around Chicago. More airspace redesigns are planned for 2003.

Although the OEP has been welcomed by airspace users, it does not go far enough or fast enough for some. As a result, there are increasing calls for more rapid and fundamental modernisation of the US air traffic management system. The drop in traffic since 11 September has not silenced the calls. Instead the lull is being seen as an opportunity to make much needed changes before traffic resumes the growth path that had taken US airspace to the verge of gridlock by the summer of 2000.

"We are moving quickly to where we may not have any choice but a revolutionary approach to modernisation," says Ron Morgan, Lockheed Martin Air Traffic Management vice-president, strategic planning. "We have to think out of the box. Airspace will not increase in volume, so we have to use it differently. We have to use more of it."

Morgan says aircraft separation standards must change from distance-based to time-based. "Today route separation is the same for large and small aircraft," he says, calling for research into new ways to separate aircraft. "Historically only radar was available. Today there is a tremendous opportunity to automate separation."

Reduced vertical separation is not the ultimate answer to increasing the available airspace, says Morgan, who believes vertical trajectory clearances should replace altitude assignments. "What the customer wants is a vertical trajectory equating to the optimum burn rate to the descent point," he says. "We can use automation to help achieve that."

Morgan believes the range of aircraft optimum performance should be broadened to make better use of airspace from 25,000ft to 50,000ft (7,600m to 15,200m). Today flights are packed into the middle altitudes because aircraft are less efficient lower down or unable to cruise higher up. Aircraft should be able to fly efficiently at 25,000ft on legs of less than 1,800km (1,000nm), he says.

Airport capacity can be increased by enabling visual procedures to be used in instrument conditions, Morgan says. At airports like San Francisco, instrument flight rules (IFR) capacity can be as little as half that in the visual flight rules (VFR). "We need to augment the vision of pilots so they can see other aircraft [in IFR]," he says, citing ADS-B and the enhanced vision system (EVS).

Runways and taxiways must be designed to reduce occupancy time, says Morgan, noting that a high-speed turn-off can reduce the time an aircraft is on the runway by 15s. This allows the spacing between arriving aircraft to be reduced or departing aircraft to be cleared more quickly. "We need better designs that reduce occupancy time because it is not realistic to build new airports," he says.

Digital voice

Morgan believes digital voice, as well as datalinks, should be used to improve communications. Datalinks are being deployed to reduce frequency congestion, but digital voice is an opportunity to improve safety, he says. "We could turn voice into information, comparing clearances with what the controller thinks is happening, and reducing operational errors caused by communications."

Information sharing and collaborative decision-making between air traffic controllers and aircraft operators should be expanded, Morgan believes. "We should tell the controller which gate the aircraft is destined for. We should provide flight plan information to air-defence co-ordinators. Airport demand information should be available to all users. Pilots should have a real-time Notam database available in the cockpit."

Ultimately, Morgan believes, elements of the national airspace system should be transitioned from ground-based to space-based "where there is a business case". Communication and navigation are already transitioning, and surveillance could follow, but not every element needs to be space-based, he says. "There has to be benefit for the user and the provider."

Increased use of space-based systems is a key feature of Boeing's vision for a future air traffic management system. The company's concept, which is being evolved with input from a wide range of "stakeholders", including the FAA, includes a new satellite constellation to complement the global positioning system (GPS) and provide communication, navigation and surveillance (CNS) services with the accuracy, integrity and availability required for safety-of-flight operations.

Satellites are a key enabler for the aircraft manufacturer's vision of a seamless global airspace system, according to Dennis Muilenburg, Boeing Air Traffic Management vice-president engineering. Although Boeing's concept starts out as a hybrid ground- and space-based system for the continental USA, it moves towards a space-based architecture as it becomes increasingly global, initially by integrating domestic and oceanic airspace then by expanding internationally.

A more space-based CNS system is one of four main features of Boeing's ATM concept, says Muilenburg. The others are the use of aircraft trajectory data to manage traffic; real-time information sharing between airspace managers and users via a common network; and simplified airspace designs and procedures. Broadband satellite communications, such as Boeing's Connexion, would be used to provide onboard trajectory data to controllers and as the backbone of the common information network.

While Boeing supports the FAA's rolling plan to increase US airspace capacity incrementally, Muilenburg says the need to boost capacity by a factor of 2.5 by 2020 requires fundamental changes. "It will require revolutionary capabilities to meet the targets," he says. The company believes it is technically feasible to implement its air traffic management concept over seven years, but acknowledges this would require extensive collaboration among the stakeholders, industry and government.

To that end, Boeing has embarked on a top-down system engineering process to understand the requirements, define the operational concept, system architecture and transition plan, and quantify the benefits. "We are taking a total system-of-systems view that is requirements-driven," says Muilenburg.

The first two phases have been completed, and involved drawing up a system requirements document with input from 39 stakeholders and then synthesising the more than 170 requirements identified into 16 "cornerstones" of a future air traffic management system.

Most recently, Boeing discussed the resulting cornerstones with 26 European stakeholders in a first step towards bringing together a global set of requirements. "We saw 80-90% commonality [between the US and European requirements]," says Muilenburg. Boeing's "working-together" efforts are continuing, with the goals of understanding the performance expectations of global stakeholders; benchmarking industry work on air traffic system operational concepts; and harmonising concepts to smooth the transition to a global system.

"The next step is the operational concept and architecture," says Muilenburg. Boeing plans to engage stakeholders over the next six to 12 months in efforts to understand the trades in areas such as system safety, security, performance, cost, transition and interoperability - described by Muilenburg as the "meat and bones" of the programme.

Boeing's baseline operational concept is trajectory-based, and exploits the aircraft's precise knowledge of where it is and where it is going to provide time-based separation management. "The capability is in aircraft today," says Muilenburg. "We can take the aircraft's trajectory and datalink it to the ground." Trajectory information will enable air traffic managers to predict where an aircraft will be further into the future and with greater precision. "We can open up the airspace," he says.

Trajectory-based air traffic management is key to coping with the anticipated proliferation of aircraft types wanting access to civil airspace, including high-speed, high-altitude airliners such as Boeing's proposed Sonic Cruiser; personal jets such as the Cessna Citation Mustang; and unmanned air vehicles such as the Northrop Grumman RQ-4 Global Hawk. Looking ahead to 2020, it is considered likely that manned and unmanned air vehicles will being sharing the same airspace.

Boeing envisages trajectory-based ATM being implemented in three phases, beginning with flow management. There would be integrated national and regional flow planning, which would be expanded in the second phase to include trajectory-based flight planning. In the third phase, trajectory information would be used to provide strategic separation assurance and allow dynamic flight replanning. The underlying information network would also be deployed in three phases, beginning with a common flow planning database that would be expanded to include flight planning and then evolved into a common airspace system database that would eventually expand on a global scale.

Transition mapping

Muilenburg acknowledges that the transition from today's radar- and flight-plan-based tactical air traffic control to a future trajectory-based strategic air traffic management system is the key issue. "Transition could be a stumbling block," he says. "It has to be addressed up front with the stakeholder group, and we are doing a lot of transition mapping today." Many of the enabling technologies are already part of the FAA's OEP. "RNP implementation is a key step," Muilenburg says.

"Working together is absolutely key," he says. "Boeing is interested in ATM because it wants to grow its commercial aircraft business, and that requires increased capacity. But the magnitude of the change required needs the co-operation of all stakeholders, as well as political guidance. We see the need for a national-level - possibly a global-level - initiative," he says.

Muilenburg's call for action at a political level has been echoed by the final report of the Commission on the Future of the US Aerospace Commission, published last month. It calls for the rapid deployment of a highly-automated air traffic management system, beyond the FAA's OEP, "so robust that it will efficiently, safely and securely accommodate an evolving variety and growing number of aerospace vehicles and civil and military operations".

"Air traffic management needs to be more robust and automated, and we need to streamline airport and runway development," says commission chairman Robert Walker. "A lot of the technology needed has already been deployed by the military," says commissioner John Douglass, president of the US Aerospace Industries Association.

"We need to organise a joint programme nationally that involves the Department of Defense, Department of Transport, NASA and the National Oceanic and Atmospheric Administration. The technology is there, but it needs to be integrated and deployed."

While the FAA is focused on implementing the Operation Evolution Plan, it is coming under increasing pressure to define long-range goals for the US airspace system. The OEP is a rolling 10-year plan, updated annually. The next iteration, setting capacity and efficiency goals reaching out to 2013, will be published in January. At the same time, the FAA is getting ready to unveil an operational concept for the airspace system of 2020.

Ops Concept 2020 has been drawn up by RTCA and approved by the Free Flight steering committee that advises the FAA on airspace modernisation. The plan will be forwarded soon to the FAA, says Charles Keegan, associate administrator for research and acquisitions. The ATM operational concept envisaged for 2020 will be used to guide future updates of the OEP, to ensure each iteration of the plan is taking the airspace system in the desired long-term direction.

Source: Flight International