Operators and regulators came together earlier in July to evaluate a key technology for 'free flight'

Graham Warwick/WASHINGTON DC


Watching the brown and purple tails descend on Wilmington, Ohio, on 10 July, an observer joked that "package wars" had broken out at Airborne Express' hub.

In fact, aircraft from rival package carriers FedEx and UPS were arriving at Wilmington to participate in the first major US operational evaluation of automatic dependent surveillance - broadcast (ADS-B), a key enabling technology for the future "free flight" air traffic management system.

That the cargo carriers' ADS-B-equipped freighters were joined at Wilmington by aircraft from the Federal Aviation Administration, NASA, US Navy, avionics manufacturers and the general aviation community is a testament to the progress of efforts to build a government/industry consensus on modernisation of the US airspace system.

"We may have started this project on our own over three years ago, but today the FAA is an indispensable element," says Steve Alterman, president of the Cargo Airline Association (CAA). The CAA's Ohio River Valley ADS-B evaluation has become part of the FAA's Safe Flight 21 programme to demonstrate and validate enabling technologies for free flight.

"The FAA has needed to be a partner with industry, and the CAA has been a big stick to prod us forward," says Shelly Meyers, director of the agency's office of communications, navigation and surveillance systems.

The three-year Safe Flight 21 effort emerged from the wreckage of the ambitious Flight 2000 programme, under which hundreds of aircraft in Alaska and Hawaii were to be equipped with FAA-supplied avionics to test a wide range of free flight technologies. "Flight 2000 was very expensive, and we never got the aviation community or Congress behind it," Meyers says.

After Congress refused to fund Flight 2000, she says, standards body RTCA offered to draw up a more modest list of airspace enhancements that industry would like to see demonstrated. Safe Flight 21 will quantify the operational benefits of the nine enhancements identified by RTCA - seven of which rely on ADS.

The Ohio River Valley operational evaluation is intended to demonstrate:

• improved terminal operations in low-visibility conditions;

• enhanced en route air-to-air operations;

• improved capability to navigate airport taxiways and;

• improved capability to see and avoid adjacent traffic.

Another major element of Safe Flight 21, the Alaska Capstone demonstration planned for next year, will involve 150-160 commercial and general aviation aircraft. This will evaluate the datalinking of weather and other information into the cockpit and an affordable means of reducing controlled flight into terrain. The remaining RTCA enhancements will be tested in other demonstrations planned before Safe Flight 21 ends in 2002, Meyers says.

For the CAA, the Ohio River Valley project is more than just an operational evaluation. Several member airlines have delayed installing the traffic alert and collision avoidance system (TCAS) in the belief that ADS-B is a better long-term solution. "We are looking towards the future, and free flight, and collision avoidance is just 5% of it," says Alterman.


The ADS-B equipment installed in the CAA aircraft for the evaluation has been developed by UPS Aviation Technologies (UPS-AT - formerly II Morrow). Airborne, FedEx and UPS have each equipped four freighters for the evaluation. The CAA hopes to gain certification for the equipment by year-end and to begin fleet-wide installation early next year.

The initial operational application will be to use ADS-B and a cockpit display of traffic information (CDTI) to improve the pilot's ability to acquire and identify other aircraft in visual conditions. This is called enhanced see and avoid and is not collision avoidance. Nevertheless, the CAA believes that this first step should improve safety at its members' hubs.


UPS believes that the enhanced see and avoid capability alone could allow the carrier to increase capacity at its Louisville, Kentucky, hub by allowing visual approach procedures to continue to lower weather minimums. "That's in the future," cautions Alterman, but CAA does plan to demonstrate and implement conflict detection and resolution using ADS-B in later phases of its programme.

Alterman says certification of an ADS-B collision avoidance capability will be "difficult". He stresses that US cargo carriers will comply with the December 2002 deadline to fit collision avoidance equipment: "All we have said is 'don't prejudice what we fit'." FedEx has decided to fit TCAS, but has told supplier Honeywell that the equipment must have ADS-B capability.

While the CAA continues to conduct an in-service evaluation of ADS-B during routine revenue operations, the Wilmington operational evaluation provided an important opportunity to test the technology. A total of 24 aircraft and one ground vehicle participated in the one-day trial, making it the biggest evaluation of ADS-B yet conducted in the USA.

In addition to the 12 CAA aircraft, three from the FAA, one each from NASA, the US Navy, Honeywell, Rockwell Collins and UPS-AT participated, plus several general aviation types. Most of the aircraft were equipped with UPS-AT's link data processor unit (LDPU) and a CDTI display produced by ADC.

The LDPU houses a global positioning system receiver and two of three candidate datalinks for ADS-B: the Mitre-designed Universal Access Transceiver (UAT) and Mode S (1090).

The third datalink candidate, the European-developed VHF Data Link (VDL) Mode 4, was not ready in time for the Wilmington demonstration, but will be evaluated as part of the CAA trial, using a radio developed by ADSI.

Meyers says a goal of Safe Flight 21 is to evaluate the performance of the three datalinks, leading to a selection by the end of 2002. This is timed to coincide with Europe's ADS-B link decision. "We are hoping for a unified, worldwide coordinated link decision," she says.

LDPU-equipped aircraft were able to transmit and receive ADS-B position reports on both the 900Mhz UAT and 1,090MHz Mode S "extended squitter" datalinks. All the CAA aircraft were also able to receive data from the FAA's traffic information system (TIS), which broadcast secondary radar data and allowed aircraft to see non-ADS-B targets.

Both ADS-B and TIS targets were displayed on the CDTI, using different symbology. ADS-B targets were displayed as chevrons with vectors indicating heading and groundspeed, arrows indicating climbing or descending and captions showing flight identity and relative altitude. The less-accurate TIS targets were represented by blunted "Pacman" symbols.

Procedures demonstrated during the day included en route station keeping using ADS-B to help the pilots maintain 15nm separation. In-trail climbs and descents and lead climbs and descents, simulating oceanic operations, were also demonstrated using ADS-B to maintain 15nm separation.


In the terminal area, CDTI was used to help pilots acquire other aircraft in the pattern visually and judge spacing, in a demonstration of the benefits of enhanced see and avoid in visual operations. Reduced visibility in the morning forced trails to be conducted in instrument conditions, and CDTI was used to enable pilots to judge spacing when they could not see the other aircraft. "This worked out very well," says Jim Cieplak, lead systems engineer at Mitre.

On the airport surface, ADS-B was used to provide pilots with situational awareness as they manoeuvred on the taxiways. CDTI showed when ADS-B-equipped aircraft were on the ground by switching from a blue chevron to a brown symbol with the caption "GROUND".

A substantial FAA-funded ground infrastructure is being put in place for the CAA's Ohio River Valley in-service evaluation. This includes ADS-B ground stations for the UAT, 1090 and VDL Mode 4 datalinks, supplied by Harris, Sensis and UPS-AT. These are being installed by Mitre and linked to a data network supplied by SITA.

UAT and 1090 ground stations at Louisville and Wilmington, supplied by Sensis and UPS-AT, were operational for the 10 July trial. Data from these sites was fused with returns from the Northrop Grumman ASR-9 primary radar at Wilmington for display on a controller's station provided by Lockheed Martin.

Further ADS-B ground stations are being installed at FedEx's Memphis, Tennessee, hub as well as the FAA's Nashville centre and Scott AFB in Illinois. The intention is to leave much of this infrastructure in place after the evaluation is complete. The CAA, backed by the FAA, certainly looks intent of pushing ahead with ADS-B.

Source: Flight International